InputMapper refactor: KeyboardInputMapper

Add a factory method for KeyboardInputMapper to be configured on
initilisation

Test: m checkinput && atest libinput_tests inputflinger_tests
Bug: 256009910
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:67ca684ad1e5d6286bdbae568ee0fc97be40d3c1)
Merged-In: Iceb8676542de85309c208af93ee7cc385e46a067
Change-Id: Iceb8676542de85309c208af93ee7cc385e46a067