Return the cursor position in screen coordinates

From its beginning, InputMethodService#onUpdateCursor has
provided the cursor position in local coordinates in the attached
view. However, the local coordinates is not useful for IMEs
to render a floating UI near the cursor because the IME is not
able to know the origin of the attached view.

With this CL, CURSOR_ANCHOR_MONITOR_MODE_CURSOR_RECT also means
that the IME will receive the cursor position in screen
coordinates. Because this is a new constant in the next release,
conditionally changing the coordinates never causes
compatibility issues as long as its behavior is well documented.

BUG: 14323360
Change-Id: I3acf2317ae1d763d11dae5ef73c2a1348b377c71