Add lock to protect UnwantedInteractionBlocker

The call to 'dump' may come from any thread, and therefore could cause a
crash. Add a lock to protect this input stage.

To run the test:
adb shell -t "/data/nativetest64/inputflinger_tests/inputflinger_tests --gtest_filter='*Dump*' --gtest_repeat=100000 --gtest_break_on_failure"

Before this patch, the test failed after ~5K - ~13K iterations (took
10-20 seconds to crash).

Bug: 232645962
Test: m inputflinger_tests && adb sync data && <run the test>
Change-Id: I2a199690450bc5bb4a8576aa59075e99d37a531b
(cherry picked from commit 9f330c54)