[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/Layer.cpp b/services/surfaceflinger/Layer.cpp
index c7d67e2..d2ab1b3 100644
--- a/services/surfaceflinger/Layer.cpp
+++ b/services/surfaceflinger/Layer.cpp
@@ -795,7 +795,8 @@
     }
 }
 
-void Layer::computeGeometry(const RenderArea& renderArea, Mesh& mesh,
+void Layer::computeGeometry(const RenderArea& renderArea,
+                            renderengine::Mesh& mesh,
                             bool useIdentityTransform) const {
     const Layer::State& s(getDrawingState());
     const ui::Transform renderAreaTransform(renderArea.getTransform());
@@ -823,7 +824,7 @@
         boundPoint(&rt, finalCrop);
     }
 
-    Mesh::VertexArray<vec2> position(mesh.getPositionArray<vec2>());
+    renderengine::Mesh::VertexArray<vec2> position(mesh.getPositionArray<vec2>());
     position[0] = renderAreaTransform.transform(lt);
     position[1] = renderAreaTransform.transform(lb);
     position[2] = renderAreaTransform.transform(rb);