Extract TouchHelper from ActivityManagerTestBase

I need the touch utility methods for WindowUntrustedTouchTest but didn't
want to inherit from ActivityManagerTestBase since that does other
things too (and because inheritance is not a good idea in general).
Also, other tests in wm test suite don't inherit from that either. So,
extracted the touch utility methods in its own function that can be used
freely by tests and left the original methods to call the delegate now,
so no test code changes.

Also added a tapOnViewCenter() that I will use in future CL.

Test: CtsWindowManagerDeviceTestCases executed by TH and pass
Bug: 158002302
Change-Id: I395dd96503b48627b4ec7ee60998150b10d44a85
2 files changed