Improve performance for certain queries/functions in REThreaded.

Some queries into RE were already thread safe, but now they are
documented as such and avoid jumping to another thread.

Additionally all void method in REThreaded are executed in an async
strategy.

Test: librenderengine_test
Bug: 184243497
Change-Id: Id04bcccf2c90acc3e6cb6f7716f9629639b757b7
diff --git a/libs/renderengine/tests/RenderEngineThreadedTest.cpp b/libs/renderengine/tests/RenderEngineThreadedTest.cpp
index 63aa4c8..b093e88 100644
--- a/libs/renderengine/tests/RenderEngineThreadedTest.cpp
+++ b/libs/renderengine/tests/RenderEngineThreadedTest.cpp
@@ -49,6 +49,9 @@
 TEST_F(RenderEngineThreadedTest, primeCache) {
     EXPECT_CALL(*mRenderEngine, primeCache());
     mThreadedRE->primeCache();
+    // need to call ANY synchronous function after primeCache to ensure that primeCache has
+    // completed asynchronously before the test completes execution.
+    mThreadedRE->getContextPriority();
 }
 
 TEST_F(RenderEngineThreadedTest, genTextures) {