Change InputReporter to InputReporterInterface

This CL changes InputReporter.h to InputReporterInterface.h to follow the
convention established with InputReader. InputReporterInterface will act
as an interface instead of a class definition, consiting only of pure
virtual methods. This makes libinputreporter more closely analogous to
libinputreader than before.

The new class, InputReporter which extends InputReporterInterface is
defined in its cpp file, InputReporter.cpp.

Bug: 119312287
Test: Build, test touch input
Change-Id: I05eb71ccec9303bd5c240e4571116f7347cafe0a