Workaround apps that make assumptions about pointer ids.

Modified the touch input mapper to assign pointer ids sequentially
starting from 0 instead of using the tracking id or slot index
supplied by the driver.  Applications should not depend on this
ordering but some do.  (sigh)

Bug: 4980884
Change-Id: I0dfeb3ac27c57a7102a13c960c760e2a02eb7669