Settings: add a new developer menu entry to show hdr/sdr ratio overlay.

- The hdr/sdr ratio overlay will be shown on screen if the option is
  selected from the developer option.
- This option is hidden on non-HDR-supported devices.
- Add flags: com.android.settings.flags.development_hdr_sdr_ratio

Test: enable show hdr/sdr ratio from developer menu; com.android.settings.development.ShowHdrSdrRatioPreferenceControllerTest
Bug: 291863102
Change-Id: Idd72f95c67c95cd8127f9b94e031b3d87b18e307

aconfig/settings_development_flag_declarations.aconfig

@@ -0,0 +1,13 @@
+package: "com.android.settings.flags"
+
+# NOTE: Keep alphabetized to help limit merge conflicts from multiple simultaneous editors.
+
+# NOTE: All Settings flags share the same Flags class, so prefix our
+# flags with 'development' to prevent naming collision.
+
+flag {
+  name: "development_hdr_sdr_ratio"
+  namespace: "core_graphics"
+  description: "Shows hdr/sdr dev opton on the development options page from aconfig"
+  bug: "291863102"
+}