Add FLAG_CURSOR_ANCHOR_INFO_IMMEDIATE support in TextView

This CL adds an initial support of
CursorAnchorInfoRequest#FLAG_CURSOR_ANCHOR_INFO_IMMEDIATE for
TextView.

This implementation is not highly optimized yet, but it just
works as it should.

BUG: 16379288
Change-Id: Iecb32b4c4dcd7db14d8b2a0d929e1d64e161bc58