Reset no focused window timeout when window gets focus

If a window is about to receive focus, then we should stop the "no
focused window" timeout.

Otherwise, we would report an ANR, even though the focused window was
added within the "dispatching timeout" grace period of the application.

Bug: 302326393
Test: TEST=inputflinger_tests; m $TEST && adb sync data && adb shell -t data/nativetest64/$TEST/$TEST --gtest_filter="*FocusedWindowWithoutSetFocusedApplication_NoAnr*" --gtest_repeat=3000 --gtest_break_on_failure
Test: TEST=inputflinger_tests; m $TEST && $ANDROID_HOST_OUT/nativetest64/$TEST/$TEST --gtest_filter="*FocusedWindowWithoutSetFocusedApplication_NoAnr" --gtest_repeat=1000 --gtest_break_on_failure
Change-Id: Ie272545e1be23ff5ef4d1bf24507a8ba7e6d170b