Add GLOBAL_STYLUS_BLOCKS_TOUCH flag

This flag will allow internal windows, like TaskBar and StatusBar, to
ignore touch while stylus is down anywhere on screen.

This is needed to reduce the chance of unintentional clicks.

Bug: 211379801
Test: TEST=inputflinger_tests; m $TEST && $ANDROID_HOST_OUT/nativetest64/$TEST/$TEST
Change-Id: I4382b390f69094b4db8928b5caf9e9251723d32e