Add unit test to cover the adaptive hold logic

Bug: 198472780
Test: events_unittests --gtest_filter="NeuralStylusPalmDetectionFilterTest.*"
Merged-In: I3364fb7a7c53ad708f815de828806239e2d3d253
Change-Id: I3364fb7a7c53ad708f815de828806239e2d3d253
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3434711
Commit-Queue: Rob Schonberger <robsc@chromium.org>
Reviewed-by: Rob Schonberger <robsc@chromium.org>
Commit-Queue: Xinglong Luan <alanlxl@chromium.org>
Cr-Commit-Position: refs/heads/main@{#967662}
(cherry picked from commit 68fb319bbf511e5dacec1593026251e2457a497c)