Support fp16 in sf

* Make sure we don't dim SDR in renderengine, and instead map HDR to the
  correct relative luminance above 1.0
* Plumb the HDR/SDR ratio into HWC

Bug: 236745178
Test: builds
Change-Id: I325972a01280d287189d38dd6c5bf7f2d4b776bb
diff --git a/services/surfaceflinger/surfaceflinger_flags.aconfig b/services/surfaceflinger/surfaceflinger_flags.aconfig
index 620ac26..fabd738 100644
--- a/services/surfaceflinger/surfaceflinger_flags.aconfig
+++ b/services/surfaceflinger/surfaceflinger_flags.aconfig
@@ -90,7 +90,6 @@
   namespace: "core_graphics"
   description: "Whether to use the closest known refresh rate to determine the fps consistency."
   bug: "299201319"
-  is_fixed_read_only: true
 }
 
 flag {
@@ -115,3 +114,11 @@
   bug: "301647974"
   is_fixed_read_only: true
 }
+
+flag {
+  name: "fp16_client_target"
+  namespace: "core_graphics"
+  description: "Controls whether we render to fp16 client targets"
+  bug: "236745178"
+  is_fixed_read_only: true
+}