Revisit nullability annotations

This commit introduces the following changes.

1) It adds a new Spring @NonNull annotation which allows to apply
@NonNullApi semantic on a specific element, like @Nullable does.
Combined with @Nullable, it allows partial null-safety support when
package granularity is too broad.

2) @Nullable and @NonNull can apply to ElementType.TYPE_USE in order
to be used on generic type arguments (SPR-15942).

3) Annotations does not apply to ElementType.TYPE_PARAMETER anymore
since it is not supported yet (applicability for such use case is
controversial and need to be discussed).

4) @NonNullApi does not apply to ElementType.FIELD anymore since in a
lot of use cases (private, protected) it is not part for the public API
+ its usage should remain opt-in. A dedicated @NonNullFields annotation
has been added in order to set fields default to non-nullable.

5) Updated Javadoc and reference documentation.

Issue: SPR-15756

spring-tx/src/main/java/org/springframework/dao/annotation/package-info.java

@@ -3,6 +3,8 @@
  * persistence exceptions based on a repository stereotype annotation.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.dao.annotation;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-tx/src/main/java/org/springframework/dao/package-info.java

@@ -14,6 +14,8 @@
  * by Rod Johnson (Wrox, 2002).
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.dao;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-tx/src/main/java/org/springframework/dao/support/package-info.java

@@ -3,6 +3,8 @@
  * providing miscellaneous utility methods.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.dao.support;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-tx/src/main/java/org/springframework/jca/cci/connection/package-info.java

@@ -4,6 +4,8 @@
  * and various simple ConnectionFactory proxies/adapters.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.jca.cci.connection;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-tx/src/main/java/org/springframework/jca/cci/core/package-info.java

@@ -3,6 +3,8 @@
  * and its associated callback interfaces.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.jca.cci.core;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-tx/src/main/java/org/springframework/jca/cci/core/support/package-info.java

@@ -3,6 +3,8 @@
  * Contains a DAO base class for CciTemplate usage.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.jca.cci.core.support;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-tx/src/main/java/org/springframework/jca/cci/object/package-info.java

@@ -6,6 +6,8 @@
  * meaning that code using this package does not need to worry about error handling.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.jca.cci.object;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-tx/src/main/java/org/springframework/jca/cci/package-info.java

@@ -5,6 +5,8 @@
  * levels of data access abstraction.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.jca.cci;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-tx/src/main/java/org/springframework/jca/context/package-info.java

@@ -3,6 +3,8 @@
  * as a JCA 1.7 compliant RAR file.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.jca.context;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-tx/src/main/java/org/springframework/jca/endpoint/package-info.java

@@ -2,6 +2,8 @@
  * This package provides a facility for generic JCA message endpoint management.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.jca.endpoint;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-tx/src/main/java/org/springframework/jca/support/package-info.java

@@ -3,6 +3,8 @@
  * mainly for local setup of a JCA ResourceAdapter and/or ConnectionFactory.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.jca.support;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-tx/src/main/java/org/springframework/jca/work/package-info.java

@@ -3,6 +3,8 @@
  * as supported within ResourceAdapters.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.jca.work;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-tx/src/main/java/org/springframework/transaction/annotation/package-info.java

@@ -4,6 +4,8 @@
  * via a special TransactionAttributeSource implementation.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.transaction.annotation;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-tx/src/main/java/org/springframework/transaction/config/package-info.java

@@ -3,6 +3,8 @@
  * with XML schema being the primary configuration format.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.transaction.config;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-tx/src/main/java/org/springframework/transaction/event/package-info.java

@@ -2,6 +2,8 @@
  * Spring's support for listening to transaction events.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.transaction.event;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-tx/src/main/java/org/springframework/transaction/interceptor/package-info.java

@@ -12,6 +12,8 @@
  * even without JTA if an application uses only a single database.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.transaction.interceptor;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-tx/src/main/java/org/springframework/transaction/jta/package-info.java

@@ -2,6 +2,8 @@
  * Transaction SPI implementation for JTA.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.transaction.jta;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-tx/src/main/java/org/springframework/transaction/package-info.java

@@ -4,6 +4,8 @@
  * Contains transaction manager, definition, and status interfaces.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.transaction;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-tx/src/main/java/org/springframework/transaction/support/package-info.java

@@ -4,6 +4,8 @@
  * and a template plus callback for transaction demarcation.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.transaction.support;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;