Reduce handwritingSlop to 2dp

To help improve the punctuation recoginization accuracy. We decided to
reduce the handwritingSlop to make it easier for user to trigger
handwriting with small strokes.

Bug: 289118001
Test: atest HandwritingInitiatorTest
Change-Id: I0f9ef38996cb061a85e415429c7ab5f86ebb22ba