Use renderengine::drawLayers api everywhere.

There's some dead code left after this change, which I'll circle around
to removing in the future.

Bug: 118461793
Bug: 123496360
Change-Id: Ic631b0c452f67b353adaa63896e8cd080e391647
Test: librenderengine_test
Test: SurfaceFlinger_test
Test: libsurfaceflinger_unittest
Test: notch hide
Test: screen rotations
Test: photos
Test: adb screencap
Test: adb screenrecord
Test: simulate virtual displays (incl. secure overlays)
Test: go/wm-smoke with gpu composition forced
diff --git a/libs/renderengine/tests/RenderEngineTest.cpp b/libs/renderengine/tests/RenderEngineTest.cpp
index bef25a8..0ee6153 100644
--- a/libs/renderengine/tests/RenderEngineTest.cpp
+++ b/libs/renderengine/tests/RenderEngineTest.cpp
@@ -194,7 +194,7 @@
 
     void clearLeftRegion();
 
-    void fillBufferThenClearRegion();
+    void clearRegion();
 
     // Dumb hack to get aroud the fact that tear-down for renderengine isn't
     // well defined right now, so we can't create multiple instances
@@ -685,14 +685,13 @@
     invokeDraw(settings, layers, mBuffer);
 }
 
-void RenderEngineTest::fillBufferThenClearRegion() {
-    fillGreenBuffer<ColorSourceVariant>();
+void RenderEngineTest::clearRegion() {
     // Reuse mBuffer
     clearLeftRegion();
     expectBufferColor(Rect(DEFAULT_DISPLAY_WIDTH / 2, DEFAULT_DISPLAY_HEIGHT), 0, 0, 0, 255);
     expectBufferColor(Rect(DEFAULT_DISPLAY_WIDTH / 2, 0, DEFAULT_DISPLAY_WIDTH,
                            DEFAULT_DISPLAY_HEIGHT),
-                      0, 255, 0, 255);
+                      0, 0, 0, 0);
 }
 
 TEST_F(RenderEngineTest, drawLayers_noLayersToDraw) {
@@ -855,8 +854,8 @@
     fillBufferWithoutPremultiplyAlpha();
 }
 
-TEST_F(RenderEngineTest, drawLayers_fillBufferThenClearRegion) {
-    fillBufferThenClearRegion();
+TEST_F(RenderEngineTest, drawLayers_clearRegion) {
+    clearRegion();
 }
 
 } // namespace android