Zero jank IMF 4/N

Convert @FlaggedApi used for flagged delegation to async:
acceptStylusHandwritingDelegation(
            @NonNull View delegateView, @NonNull String delegatorPackageName,
            @HandwritingDelegateFlags int flags)

Test: atest StylusHandwritingTest
Bug: 293640003

Change-Id: Ib5d1e9d1da1c9ba20e3da518ef881202de742488