Deprecated unused/obsolete mutable APIs, to be removed in next breaking change.

These APIs were intended to support an internal-only mutable implementation of Java protobuf and should not actually be used in open source. Removal of these APIs shouldn't break anyone -- the equivalent immutable methods should be used instead.

PiperOrigin-RevId: 651833683

Author: zhangskz

java/core/src/main/java/com/google/protobuf/ExtensionRegistry.java

@@ -126,6 +126,7 @@ public ExtensionInfo findImmutableExtensionByName(final String fullName) {
    *
    * @return Information about the extension if found, or {@code null} otherwise.
    */
+  @Deprecated
   public ExtensionInfo findMutableExtensionByName(final String fullName) {
     return mutableExtensionsByName.get(fullName);
   }
@@ -152,6 +153,7 @@ public ExtensionInfo findImmutableExtensionByNumber(
    *
    * @return Information about the extension if found, or {@code null} otherwise.
    */
+  @Deprecated
   public ExtensionInfo findMutableExtensionByNumber(
       final Descriptor containingType, final int fieldNumber) {
     return mutableExtensionsByNumber.get(new DescriptorIntPair(containingType, fieldNumber));
@@ -163,6 +165,7 @@ public ExtensionInfo findMutableExtensionByNumber(
    *
    * @return Information about the extensions found, or {@code null} if there are none.
    */
+  @Deprecated
   public Set<ExtensionInfo> getAllMutableExtensionsByExtendedType(final String fullName) {
     HashSet<ExtensionInfo> extensions = new HashSet<ExtensionInfo>();
     for (DescriptorIntPair pair : mutableExtensionsByNumber.keySet()) {