API Review: CursorAnchorInfo

This CL introduces following combinable flags as a replacement
of CHARACTER_RECT_TYPE_* constants.
- CursorAnchorInfo.FLAG_HAS_VISIBLE_REGION
- CursorAnchorInfo.FLAG_HAS_INVISIBLE_REGION

This CL also replaces #isInsertionMarkerClipped() with
flags.

Rationale:
getCharacterRectFlags() should return a set of flags, rather
than enum-like types.

getInsertionMarkerFlags() is more consistent with
getCharacterRectFlags() than isInsertionMarkerClipped().
It is also open for future extension.

BUG: 17200900
Change-Id: Ia8cbb9f6b41cd9509fc0147fd68763dfde593ffc