Render `FILE` instead of `File` for new diffs

During the rollout it will be very beneficial, if we can tell apart
users that are using the old diff vs the new diff. Rendering `FILE` as
the line number instead of `File` in the top most row seems to be
appropriate, because no one will notice, but we will still have a clear
indicator. :-)

Release-Notes: skip
Change-Id: Ib0a8f6737d6b4126000b3b7c8c8247941fccc326
diff --git a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row.ts b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row.ts
index 52b1467..8ef2f82 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row.ts
@@ -364,7 +364,7 @@
           fire(this, 'line-mouse-enter', {lineNum: lineNumber, side})}
         @mouseleave=${() =>
           fire(this, 'line-mouse-leave', {lineNum: lineNumber, side})}
-      >${lineNumber === FILE ? 'File' : lineNumber.toString()}</button>
+      >${lineNumber === FILE ? 'FILE' : lineNumber.toString()}</button>
     `;
   }
 
diff --git a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-element_test.ts b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-element_test.ts
index 910575c..56336f0 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-element_test.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-element_test.ts
@@ -122,7 +122,7 @@
                       id="left-button-FILE"
                       tabindex="-1"
                     >
-                      File
+                      FILE
                     </button>
                   </td>
                   <td class="gr-diff lineNum right" data-value="FILE">
@@ -133,7 +133,7 @@
                       id="right-button-FILE"
                       tabindex="-1"
                     >
-                      File
+                      FILE
                     </button>
                   </td>
                   <td
@@ -1368,7 +1368,7 @@
                       id="left-button-FILE"
                       tabindex="-1"
                     >
-                      File
+                      FILE
                     </button>
                   </td>
                   <td class="gr-diff left no-intraline-info sign"></td>
@@ -1383,7 +1383,7 @@
                       id="right-button-FILE"
                       tabindex="-1"
                     >
-                      File
+                      FILE
                     </button>
                   </td>
                   <td class="gr-diff no-intraline-info right sign"></td>
@@ -2965,7 +2965,7 @@
                         id="left-button-FILE"
                         tabindex="-1"
                       >
-                        File
+                        FILE
                       </button>
                     </td>
                     <td class="gr-diff left no-intraline-info sign"></td>
@@ -2980,7 +2980,7 @@
                         id="right-button-FILE"
                         tabindex="-1"
                       >
-                        File
+                        FILE
                       </button>
                     </td>
                     <td class="gr-diff no-intraline-info right sign"></td>