[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.cpp b/services/surfaceflinger/DisplayHardware/HWC2.cpp
index 393041d..b4ac506 100644
--- a/services/surfaceflinger/DisplayHardware/HWC2.cpp
+++ b/services/surfaceflinger/DisplayHardware/HWC2.cpp
@@ -538,6 +538,14 @@
     return Error::None;
 }
 
+Error Display::getDisplayedContentSamplingAttributes(PixelFormat* outFormat,
+                                                     Dataspace* outDataspace,
+                                                     uint8_t* outComponentMask) const {
+    auto intError = mComposer.getDisplayedContentSamplingAttributes(mId, outFormat, outDataspace,
+                                                                    outComponentMask);
+    return static_cast<Error>(intError);
+}
+
 Error Display::getReleaseFences(
         std::unordered_map<Layer*, sp<Fence>>* outFences) const
 {