Support fp16 in hwui for HDR

Picking sRGB primaries and transfer with extended range bit as the
dataspace, because that's straightforward for EGL.

Then, rather than dimming SDR content, we instead just render as normal
so that we take advantage of the full bit depth

Bug: 236745178
Test: builds
Change-Id: Ica39a2c81be508effb97a8850b0c8e272c10a084