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-jdbc/src/main/java/org/springframework/jdbc/config/package-info.java

@@ -2,6 +2,8 @@
  * Defines the Spring JDBC configuration namespace.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.jdbc.config;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/package-info.java

@@ -2,6 +2,8 @@
  * Context metadata abstraction for the configuration and execution of a stored procedure call.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.jdbc.core.metadata;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-jdbc/src/main/java/org/springframework/jdbc/core/namedparam/package-info.java

@@ -11,6 +11,8 @@
  * work with the returned classic template, or use a JdbcTemplate instance directly.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.jdbc.core.namedparam;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-jdbc/src/main/java/org/springframework/jdbc/core/package-info.java

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

spring-jdbc/src/main/java/org/springframework/jdbc/core/simple/package-info.java

@@ -6,6 +6,8 @@
  * parameter specification becomes unnecessary since it can be looked up in the metadata.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.jdbc.core.simple;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-jdbc/src/main/java/org/springframework/jdbc/core/support/package-info.java

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

spring-jdbc/src/main/java/org/springframework/jdbc/datasource/embedded/package-info.java

@@ -2,6 +2,8 @@
  * Provides extensible support for creating embedded database instances.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.jdbc.datasource.embedded;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-jdbc/src/main/java/org/springframework/jdbc/datasource/init/package-info.java

@@ -2,6 +2,8 @@
  * Provides extensible support for initializing databases through scripts.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.jdbc.datasource.init;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-jdbc/src/main/java/org/springframework/jdbc/datasource/lookup/package-info.java

@@ -2,6 +2,8 @@
  * Provides a strategy for looking up JDBC DataSources by name.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.jdbc.datasource.lookup;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-jdbc/src/main/java/org/springframework/jdbc/datasource/package-info.java

@@ -4,6 +4,8 @@
  * and various simple DataSource implementations.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.jdbc.datasource;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-jdbc/src/main/java/org/springframework/jdbc/object/package-info.java

@@ -15,6 +15,8 @@
  * by Rod Johnson (Wrox, 2002).
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.jdbc.object;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-jdbc/src/main/java/org/springframework/jdbc/package-info.java

@@ -18,6 +18,8 @@
  * by Rod Johnson (Wrox, 2002).
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.jdbc;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-jdbc/src/main/java/org/springframework/jdbc/support/lob/package-info.java

@@ -3,6 +3,8 @@
  * as well as a customizable default implementation.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.jdbc.support.lob;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

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

@@ -7,6 +7,8 @@
  * or in JDBC-based O/R mapping layers.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.jdbc.support;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-jdbc/src/main/java/org/springframework/jdbc/support/rowset/package-info.java

@@ -3,6 +3,8 @@
  * Supported by JdbcTemplate, but can be used independently too.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.jdbc.support.rowset;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-jdbc/src/main/java/org/springframework/jdbc/support/xml/package-info.java

@@ -2,6 +2,8 @@
  * Abstraction for handling fields of SQLXML data type.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.jdbc.support.xml;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;