Add missing package-info files for common packages

Issue: SPR-14420

spring-context/src/main/java/org/springframework/validation/beanvalidation/package-info.java

 /**
  * Support classes for integrating a JSR-303 Bean Validation provider
- * (such as Hibernate Validator 4.0) into a Spring ApplicationContext
+ * (such as Hibernate Validator) into a Spring ApplicationContext
  * and in particular with Spring's data binding and validation APIs.
  *
  * <p>The central class is {@link

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

 /**
  * Spring's repackaging of
- * <a href="http://cglib.sourceforge.net">net.sf.cglib 3.1</a>
+ * <a href="http://cglib.sourceforge.net">net.sf.cglib 3.2</a>
  * (for internal use only).
  *
  * <p>This repackaging technique avoids any potential conflicts with
@@ -9,7 +9,7 @@
  *
  * <p>As this repackaging happens at the class file level, sources
  * and javadocs are not available here. See the original
- * <a href="http://cglib.sourceforge.net/apidocs">CGLIB 3.1 javadocs</a>
+ * <a href="http://cglib.sourceforge.net/apidocs">CGLIB 3.2 javadocs</a>
  * for details when working with these classes.
  */
 package org.springframework.cglib;

spring-expression/src/main/java/org/springframework/expression/common/package-info.java

+/**
+ * Common utility classes behind the <em>Spring Expression Language</em>.
+ */
+package org.springframework.expression.common;

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

+/**
+ * Core abstractions behind the <em>Spring Expression Language</em>.
+ */
+package org.springframework.expression;

spring-expression/src/main/java/org/springframework/expression/spel/ast/package-info.java

+/**
+ * SpEL's abstract syntax tree.
+ */
+package org.springframework.expression.spel.ast;

spring-expression/src/main/java/org/springframework/expression/spel/package-info.java

+/**
+ * SpEL's central implementation package.
+ */
+package org.springframework.expression.spel;

spring-expression/src/main/java/org/springframework/expression/spel/standard/package-info.java

+/**
+ * SpEL's standard parser implementation.
+ */
+package org.springframework.expression.spel.standard;

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

+/**
+ * SpEL's default implementations for various core abstractions.
+ */
+package org.springframework.expression.spel.support;

spring-test/src/main/java/org/springframework/test/context/cache/package-info.java

+/**
+ * Support for context caching within the <em>Spring TestContext Framework</em>.
+ */
+package org.springframework.test.context.cache;

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

 /**
- * Java 5 annotation for transaction demarcation.
+ * Spring's support for annotation-based transaction demarcation.
  * Hooked into Spring's transaction interception infrastructure
  * via a special TransactionAttributeSource implementation.
  */

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

+/**
+ * Spring's support for listening to transaction events.
+ */
+package org.springframework.transaction.event;

spring-web/src/main/java/org/springframework/http/converter/json/package-info.java

 /**
- * Provides an HttpMessageConverter implementations for handling JSON.
+ * Provides HttpMessageConverter implementations for handling JSON.
  */
 package org.springframework.http.converter.json;

spring-web/src/main/java/org/springframework/http/converter/protobuf/package-info.java

+/**
+ * Provides an HttpMessageConverter implementation for handling
+ * <a href="https://developers.google.com/protocol-buffers/">Google Protocol Buffers</a>.
+ */
+package org.springframework.http.converter.protobuf;

spring-web/src/main/java/org/springframework/http/converter/support/package-info.java

+/**
+ * Provides a comprehensive HttpMessageConverter variant for form handling.
+ */
+package org.springframework.http.converter.support;

spring-web/src/main/java/org/springframework/http/converter/xml/package-info.java

 /**
- * Provides an HttpMessageConverter implementations for handling XML.
+ * Provides HttpMessageConverter implementations for handling XML.
  */
 package org.springframework.http.converter.xml;

spring-web/src/main/java/org/springframework/web/context/annotation/package-info.java

+/**
+ * Provides convenience annotations for web scopes.
+ */
+package org.springframework.web.context.annotation;