Input: Add isStylusToolType() utility function

Using this utility function will ensure we don't forget to check for
both TOOL_TYPE_STYLUS and TOOL_TYPE_ERASER when we are looking to
identify a stylus.

This will cause a behavior change in UnwantedInteractionBlocker, where
TOOL_TYPE_ERASER was not previously considered a stylus tool.

Bug: None
Test: atest inputflinger_tests
Change-Id: I3dae9b5037d7ac08a5672c6e4d6e3b62ee2bd352