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-beans/src/main/java/org/springframework/beans/annotation/package-info.java

@@ -2,6 +2,8 @@
  * Support package for beans-style handling of Java 5 annotations.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.beans.annotation;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-beans/src/main/java/org/springframework/beans/factory/annotation/package-info.java

@@ -2,6 +2,8 @@
  * Support package for annotation-driven bean configuration.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.beans.factory.annotation;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-beans/src/main/java/org/springframework/beans/factory/config/package-info.java

@@ -2,6 +2,8 @@
  * SPI interfaces and configuration-related convenience classes for bean factories.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.beans.factory.config;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-beans/src/main/java/org/springframework/beans/factory/package-info.java

@@ -10,6 +10,8 @@
  * by Rod Johnson (Wrox, 2002).
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.beans.factory;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-beans/src/main/java/org/springframework/beans/factory/parsing/package-info.java

@@ -2,6 +2,8 @@
  * Support infrastructure for bean definition parsing.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.beans.factory.parsing;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-beans/src/main/java/org/springframework/beans/factory/serviceloader/package-info.java

@@ -2,6 +2,8 @@
  * Support package for the Java 6 ServiceLoader facility.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.beans.factory.serviceloader;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

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

@@ -3,6 +3,8 @@
  * Contains abstract base classes for {@code BeanFactory} implementations.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.beans.factory.support;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-beans/src/main/java/org/springframework/beans/factory/wiring/package-info.java

@@ -3,6 +3,8 @@
  * Foundation for aspect-driven bean configuration.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.beans.factory.wiring;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-beans/src/main/java/org/springframework/beans/factory/xml/package-info.java

@@ -3,6 +3,8 @@
  * including a standard "spring-beans" XSD.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.beans.factory.xml;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

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

@@ -10,6 +10,8 @@
  * by Rod Johnson (Wrox, 2002).
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.beans;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-beans/src/main/java/org/springframework/beans/propertyeditors/package-info.java

@@ -7,6 +7,8 @@
  * specific binding processes, as they are localized or the like.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.beans.propertyeditors;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

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

@@ -3,6 +3,8 @@
  * such as utility classes for sorting and holding lists of beans.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.beans.support;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;