Add missing package-info files for common packages

Issue: SPR-14420
(cherry picked from commit 66ec1c1)

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

@@ -1,4 +1,4 @@
 /**
- * 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

@@ -0,0 +1,5 @@
+/**
+ * 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

@@ -0,0 +1,4 @@
+/**
+ * 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

@@ -1,4 +1,4 @@
 /**
- * Provides an HttpMessageConverter implementations for handling XML.
+ * Provides HttpMessageConverter implementations for handling XML.
  */
 package org.springframework.http.converter.xml;