Rename files to preserve history

Test\Eslint fail - this is expected.

Change-Id: I44a2d9c6c11d0757f948f1a278bce599691da872
diff --git a/polygerrit-ui/app/elements/diff/gr-syntax-layer/gr-syntax-layer.js b/polygerrit-ui/app/elements/diff/gr-syntax-layer/gr-syntax-layer.ts
similarity index 100%
rename from polygerrit-ui/app/elements/diff/gr-syntax-layer/gr-syntax-layer.js
rename to polygerrit-ui/app/elements/diff/gr-syntax-layer/gr-syntax-layer.ts