[DO NOT MERGE] Fix Stylus CTS by checking startInput

check onStartInput() before injecting stylus events.
Note: we don't need to port this to master as it already has this fix.

Bug: 241000301
Test: atest StylusHandwritingTest#testHandwritingStartAndFinish
Change-Id: Id9504c34dbe4990fab11ad9bef9ed7129daf97d8
1 file changed