Fix: Handwriting only initiate for the first time

Handwriting initiator accidentally changes the View's handwriting area.
As a result, it stops working after startHandwriting is called for the
View once. This CL fixed the issue by not exposing the internal
handwriting area Rect object in the View.

Bug: 222117485
Test: manually tested
Change-Id: I5cb6231361fbd7566edddb1aebf7b99330c3a8d8