Rename file to preserve history

Change-Id: I5a358320bfdc494446d46bf0cf538a9479ee238c
diff --git a/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread_test.js b/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread_test.ts
similarity index 100%
rename from polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread_test.js
rename to polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread_test.ts