ChangeScreen2: Add key binding for Expand All/Collapse All buttons

eb924ff74a inroduced one of the most wanted
features, that the whole community has been waiting for years. Let's add
key bindings for that too.

Change-Id: I9b159a9a877cf95edd1628329a9448de3a59fe21
(cherry picked from commit 79f675a5a5)

gerrit-gwtui/src/main/java/com/google/gerrit/client/change/ChangeScreen2.java

@@ -250,6 +250,18 @@ public class ChangeScreen2 extends Screen {
         }
       }
     });
+    keysAction.add(new KeyCommand(0, 'x', Util.C.keyExpandAllMessages()) {
+      @Override
+      public void onKeyPress(KeyPressEvent event) {
+        onExpandAll(null);
+      }
+    });
+    keysAction.add(new KeyCommand(0, 'z', Util.C.keyCollapseAllMessages()) {
+      @Override
+      public void onKeyPress(KeyPressEvent event) {
+        onCollapseAll(null);
+      }
+    });
     if (Gerrit.isSignedIn()) {
       keysAction.add(new KeyCommand(0, 's', Util.C.changeTableStar()) {
         @Override

gerrit-gwtui/src/main/java/com/google/gerrit/client/changes/ChangeConstants.java

@@ -62,6 +62,8 @@ public interface ChangeConstants extends Constants {
   String keyEditTopic();
   String keyEditMessage();
   String keyAddReviewers();
+  String keyExpandAllMessages();
+  String keyCollapseAllMessages();
 
   String patchTableColumnName();
   String patchTableColumnComments();

gerrit-gwtui/src/main/java/com/google/gerrit/client/changes/ChangeConstants.properties

@@ -42,6 +42,8 @@ keyPublishComments = Review and publish comments
 keyEditTopic = Edit change topic
 keyEditMessage = Edit commit message
 keyAddReviewers = Add reviewers
+keyExpandAllMessages = Expand all messages
+keyCollapseAllMessages = Collapse all messages
 
 
 patchTableColumnName = File Path