graphics: make mapper default impl a header library

Reimplement the default impl as a header-only library,
android.hardware.graphics.mapper@2.0-passthrough, based on the HAL
support library.

Effectively, this renames Gralloc[01]Mapper to Gralloc[01]Hal, and
make adjustments here and there to meet the requirements of the HAL
support library.  This also adds GrallocLoader to load either of
Gralloc[01]Hal and create an IMapper instance.

libgrallocmapperincludes is renamed to follow the new naming and
include path conventions.

Test: boots and VTS
Change-Id: I924cadce9a10a6e544f99ceba63aadc38ec431ac