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

res/values/strings.xml

@@ -1853,6 +1853,11 @@
     <!-- Debugging developer settings: show refresh rate summary [CHAR LIMIT=58] -->
     <string name="show_refresh_rate_summary">Show the current display refresh rate</string>
 
+    <!-- Debugging developer settings: show HDR/SDR ratio? [CHAR LIMIT=36] -->
+    <string name="show_hdr_sdr_ratio">Show HDR/SDR ratio</string>
+    <!-- Debugging developer settings: show HDR/SDR ratio summary [CHAR LIMIT=58] -->
+    <string name="show_hdr_sdr_ratio_summary">Show the current HDR/SDR ratio</string>
+
     <!-- NFC settings -->
     <!-- Used in the 1st-level settings screen to turn on NFC -->
     <string name="nfc_quick_toggle_title">NFC</string>

res/xml/development_settings.xml

@@ -273,6 +273,11 @@
             android:title="@string/show_refresh_rate"
             android:summary="@string/show_refresh_rate_summary" />
 
+        <SwitchPreferenceCompat
+            android:key="show_hdr_sdr_ratio"
+            android:title="@string/show_hdr_sdr_ratio"
+            android:summary="@string/show_hdr_sdr_ratio_summary" />
+
         <SwitchPreferenceCompat
             android:key="overlay_settings"
             android:title="@string/overlay_settings_title"