[SurfaceFlinger] add getDisplayedContentSamplingAttributes i/f

Add interface to ISurfaceComposer that can query the
graphics.composer for querying the displayed content sampling
engine's supported attributes.

Bug: 116028618
Test: Boot
Test: ran test client against prototype, see attributes reported
Test: Ran new test './libgui_test  --gtest_filter="DisplayedContentSamp*"'
Test: on hwc with and without new function hook.
Change-Id: Ie4bebd98d134e63a9f3e21f79ae519a1fe8055b0
diff --git a/services/surfaceflinger/DisplayHardware/HWC2.h b/services/surfaceflinger/DisplayHardware/HWC2.h
index d274631..607d9ef 100644
--- a/services/surfaceflinger/DisplayHardware/HWC2.h
+++ b/services/surfaceflinger/DisplayHardware/HWC2.h
@@ -237,6 +237,9 @@
     [[clang::warn_unused_result]] Error supportsDoze(bool* outSupport) const;
     [[clang::warn_unused_result]] Error getHdrCapabilities(
             android::HdrCapabilities* outCapabilities) const;
+    [[clang::warn_unused_result]] Error getDisplayedContentSamplingAttributes(
+            android::ui::PixelFormat* outFormat, android::ui::Dataspace* outDataspace,
+            uint8_t* outComponentMask) const;
     [[clang::warn_unused_result]] Error getReleaseFences(
             std::unordered_map<Layer*,
                     android::sp<android::Fence>>* outFences) const;