[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/BufferLayer.h b/services/surfaceflinger/BufferLayer.h
index 3d06ded..45906ff 100644
--- a/services/surfaceflinger/BufferLayer.h
+++ b/services/surfaceflinger/BufferLayer.h
@@ -178,7 +178,7 @@
     bool mBufferLatched; // TODO: Use mActiveBuffer?
 
     // The texture used to draw the layer in GLES composition mode
-    mutable Texture mTexture;
+    mutable renderengine::Texture mTexture;
 
     bool mRefreshPending;
 };