Implement ThreadedInputConnection#getCursorCapsMode()

Some Latin keyboard apps use this function to check whether they need to
capitalize a letter at the current cursor. Delegating to TextUtil just as
BaseInputConnection#getCursorCapsMode() does.

BUG=648439

Review-Url: https://codereview.chromium.org/2349383004
Cr-Commit-Position: refs/heads/master@{#419929}