Move displayid into InputEvent

There are certain use cases where key events should be associated with a
particular display. Refactor KeyEvent and MotionEvent to have an
associated display id.

Remove "hasAssociatedDisplay" variable from KeyboardInputMapper,
it just used to mirror "isOrientationAware".

If the keyboard is orientation aware (= it is physically attached to a
display, and therefore rotates together with that display), then
associate that keyboard with the internal viewport. Otherwise, the key
events are not associated with any particular display.

Remaining to do:
- make mInternalDisplay, mExternalDisplay, mVirtualDisplays into a
single vector with type (internal, external, virtual)
- have getDisplayViewport return std::optional (will require deep
changes)

Bug: 64258305
Test: atest inputflinger_tests libinput_tests

Change-Id: I4fe145e74cb59310efaa55bfc9dc3c2b3bd997e3