Make toString(), hashCode(), equals() and friends final in AutoValue classes

Developers usually don't look at the classes that AutoValue generates,
but at the hand-written classes. If the hand-written classes implement
toString(), hashCode(), equals() etc, AutoValue doesn't override them.
To make this more clear to readers of the hand-written classes
ErrorProne suggests to make these methods final.

See https://errorprone.info/bugpattern/AutoValueFinalMethods

Enable this check at ERROR severity to prevent future occurrences.

Signed-off-by: Edwin Kempin <ekempin@google.com>
Change-Id: I972e8e8f9339b811c78157abef771b8c32be079c

java/com/google/gerrit/server/account/externalids/ExternalId.java

@@ -193,7 +193,7 @@ public abstract class ExternalId implements Serializable {
     }
 
     @Override
-    public String toString() {
+    public final String toString() {
       return get();
     }
 
@@ -441,7 +441,7 @@ public abstract class ExternalId implements Serializable {
    * that was loaded from Git can be equal with an external ID that was created from code.
    */
   @Override
-  public boolean equals(Object obj) {
+  public final boolean equals(Object obj) {
     if (!(obj instanceof ExternalId)) {
       return false;
     }
@@ -453,7 +453,7 @@ public abstract class ExternalId implements Serializable {
   }
 
   @Override
-  public int hashCode() {
+  public final int hashCode() {
     return Objects.hash(key(), accountId(), email(), password());
   }
 
@@ -471,7 +471,7 @@ public abstract class ExternalId implements Serializable {
    * </pre>
    */
   @Override
-  public String toString() {
+  public final String toString() {
     Config c = new Config();
     writeToConfig(c);
     return c.toText();