Rename files to preserve history

Test\Eslint fail - this is expected.

Change-Id: I7b791a9f16249de59a37da118e38c7c682b2724d
diff --git a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.js b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.ts
similarity index 100%
rename from polygerrit-ui/app/elements/diff/gr-diff/gr-diff.js
rename to polygerrit-ui/app/elements/diff/gr-diff/gr-diff.ts