Rename files to preserve history

Test\Eslint fail - this is expected.

Change-Id: I5c8e19b1ed397f50fefb715a1d68ac65da9b67de
diff --git a/polygerrit-ui/app/elements/plugins/gr-plugin-host/gr-plugin-host.js b/polygerrit-ui/app/elements/plugins/gr-plugin-host/gr-plugin-host.ts
similarity index 100%
rename from polygerrit-ui/app/elements/plugins/gr-plugin-host/gr-plugin-host.js
rename to polygerrit-ui/app/elements/plugins/gr-plugin-host/gr-plugin-host.ts