Convert TouchInputMapper enums to enum classes.

Also, drop virtual for override methods. The override keyword requires
a method to both be virtual and overriding a parent's virtual method, so
having both is redundant.

Bug: 160010896
Test: atest InputReader_test.cpp
Change-Id: Ia36e0fa95068531e5e23c3932b7c190dfa40ecd9
Merged-In: Ia36e0fa95068531e5e23c3932b7c190dfa40ecd9