Rename files to preserve history

Test\Eslint fail - this is expected.

Change-Id: I59bdcf908d897512988ee2fe8352dfa270dab18b
diff --git a/polygerrit-ui/app/elements/change-list/gr-user-header/gr-user-header.js b/polygerrit-ui/app/elements/change-list/gr-user-header/gr-user-header.ts
similarity index 100%
rename from polygerrit-ui/app/elements/change-list/gr-user-header/gr-user-header.js
rename to polygerrit-ui/app/elements/change-list/gr-user-header/gr-user-header.ts