Support extended range fp16 ClientTargets in HWC

Introduce the concept of hdrSdrRatio for ClientTargets, so that:

* 1.0 is treated as SDR luminance
* hdrSdrRatio is provided to scale the content into display luminance
  range during composition. That is, 1.0 maps to SDR max, and
  hdrSdrRatio maps to display max luminance

Bug: 236745178
Test: builds
Change-Id: Id82a102eaca82f85bf3982538786dd2ae6cb8e61