[RenderEngine] Organize RenderEngine directory.

This patch:
1. adds proper namespace renderengine to all RenderEngine code,
   and namespace gl to all GLES related code
2. creates gl/ directory for GLES backend code
3. Reorder include header files, remove unused header files.

BUG: 112585051
Test: Build, flash, run display validation
Change-Id: I81f0b8831213607cde08562958f7c38ddaf4c9e6
diff --git a/services/surfaceflinger/RenderEngine/Mesh.cpp b/services/surfaceflinger/RenderEngine/Mesh.cpp
index 43852eb..5a3c2c8 100644
--- a/services/surfaceflinger/RenderEngine/Mesh.cpp
+++ b/services/surfaceflinger/RenderEngine/Mesh.cpp
@@ -19,6 +19,7 @@
 #include <utils/Log.h>
 
 namespace android {
+namespace renderengine {
 
 Mesh::Mesh(Primitive primitive, size_t vertexCount, size_t vertexSize, size_t texCoordSize)
       : mVertexCount(vertexCount),
@@ -94,4 +95,5 @@
     return mStride;
 }
 
-} /* namespace android */
+}  // namespace renderengine
+}  // namespace android