Make RenderEngine render to the same format as the readback buffer.

Some device's readback buffers do not support alpha, so rendering golden
images should also not use alpha.

Bug: 335805098
Test: VtsHalGraphicsComposer3_ReadbackTest
Change-Id: I153ea1707b9fd8113529b8c18fa90711acfad04e
diff --git a/graphics/composer/aidl/vts/VtsHalGraphicsComposer3_ReadbackTest.cpp b/graphics/composer/aidl/vts/VtsHalGraphicsComposer3_ReadbackTest.cpp
index d4ce3ba..3d9253f 100644
--- a/graphics/composer/aidl/vts/VtsHalGraphicsComposer3_ReadbackTest.cpp
+++ b/graphics/composer/aidl/vts/VtsHalGraphicsComposer3_ReadbackTest.cpp
@@ -59,10 +59,12 @@
 
         EXPECT_TRUE(mComposerClient->setPowerMode(getPrimaryDisplayId(), PowerMode::ON).isOk());
 
+        const auto format = getHasReadbackBuffer() ? mPixelFormat : common::PixelFormat::RGBA_8888;
+
         ASSERT_NO_FATAL_FAILURE(
                 mTestRenderEngine = std::unique_ptr<TestRenderEngine>(new TestRenderEngine(
                         ::android::renderengine::RenderEngineCreationArgs::Builder()
-                                .setPixelFormat(static_cast<int>(common::PixelFormat::RGBA_8888))
+                                .setPixelFormat(static_cast<int>(format))
                                 .setImageCacheSize(TestRenderEngine::sMaxFrameBufferAcquireBuffers)
                                 .setEnableProtectedContext(false)
                                 .setPrecacheToneMapperShaderOnly(false)