[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/LayerBE.cpp b/services/surfaceflinger/LayerBE.cpp
index f389b57..da98bf5 100644
--- a/services/surfaceflinger/LayerBE.cpp
+++ b/services/surfaceflinger/LayerBE.cpp
@@ -30,14 +30,14 @@
 
 LayerBE::LayerBE(Layer* layer, std::string layerName)
       : mLayer(layer),
-        mMesh(Mesh::TRIANGLE_FAN, 4, 2, 2) {
+        mMesh(renderengine::Mesh::TRIANGLE_FAN, 4, 2, 2) {
     compositionInfo.layer = std::make_shared<LayerBE>(*this);
     compositionInfo.layerName = layerName;
 }
 
 LayerBE::LayerBE(const LayerBE& layer)
       : mLayer(layer.mLayer),
-        mMesh(Mesh::TRIANGLE_FAN, 4, 2, 2) {
+        mMesh(renderengine::Mesh::TRIANGLE_FAN, 4, 2, 2) {
     compositionInfo.layer = layer.compositionInfo.layer;
     compositionInfo.layerName = layer.mLayer->getName().string();
 }
@@ -48,7 +48,7 @@
     }
 }
 
-void LayerBE::clear(RE::RenderEngine& engine) {
+void LayerBE::clear(renderengine::RenderEngine& engine) {
     engine.setupFillWithColor(0, 0, 0, 0);
     engine.drawMesh(mMesh);
 }