Revert "Revert "Scribe in IMF: startStylusHandwriting & lifecycl..."

Revert^2 "CTS for Stylus Handwriting lifecycle"

493b8d7d3b4d43e483c03b155d38057e3eacd3c9

Reason: Fix API signature related issues by making newly introduced
 methods in InputMethod.java default

Bug: 213976598
Bug: 203086136
Test: atest StylusHandwritingTest
Test: atest SignatureTest#testSignature

Change-Id: Idfd5d1f84e66e3a19ef384589b4892adb91f8066