Prevent scrolling for handwriting delegator

When stylus movement occurs on a handwriting delegator view, there may
be some latency before the handwriting session starts. During this
latency, the stylus movement should not cause scrolling. This can be
suppressed in the same way that was done for standard handwriting
initiation.

Bug: 228210945
Test: atest android.view.stylus.HandwritingInitiatorTest
Change-Id: Ibafb6031f87fb1b1c1c9e4cfd679eb09b69b8f2a