Make tempTouchState a local variable

Currently, mTempTouchState is a class variable, and it is confusing when
it is being modified in functions such as findTouchedWindowAt.

This variable is only used inside findTouchedWindowTargets, so convert
it to a local variable. This will make it easier to keep track of its
contents.

Bug: none
Test: none
Change-Id: I8b4f45eadf0ba05e5979de39f78ba81fe79bce31