Re-use existing thread

Bug: 7377541
Change-Id: I097f2288ebfc2b4a9782cbced19d9c36d0703acb
Reduce jankiness of the transition between a text field with FLAG_NO_FULLSCREEN and a text field with FLAG_NO_EXTRACT_UI

Bug: 7393485

Currently, the extract text view blinks at the transition of InputMethodService.
This change reduces this blinking by making the extract text view invisible when the extract text view is hidden.

Change-Id: I9af96058283a9a5b60707d025ad1abbbbc23c16f
Optimize drawHardwareAccelerated method in Editor class

When inserting a new line or breaking a line,
every display list was invalidated and rebuilt before.
However, we can reuse the display lists above intactly and also
reuse the display lists below with only updating drawing locations.

This patch reuses the display lists if possible.
The display lists above the inserted line are just reused
and the display lists below are reused with only updating
drawing locations not fullly rebuilt.

mIndexOfFirstChangedBlock is the index of the first block
which is moved by inserting or breaking a line.
So the display list whose index is >= mIndexOfFirstChangedBlock
only needs to update its drawing location.

Change-Id: Ica20deb0ebb5750de21356ed31fa9f86e657ff92
Signed-off-by: Sangkyu Lee <sk82.lee@lge.com>