[RenderEngine] Remove overrided methods with GLES implementation from public.

This patch moves all overrided methods with GLES implementation from
impl::RenderEngine to GLES20RenderEngine.

BUG: 112585051
Test: Build, flash, boot and do part of display verification.
Change-Id: I2b70d77887931a060c6bf5eff0fad23e9f3ab5e2
diff --git a/services/surfaceflinger/RenderEngine/gl/GLES20RenderEngine.h b/services/surfaceflinger/RenderEngine/gl/GLES20RenderEngine.h
index 3113e53..04dc1b1 100644
--- a/services/surfaceflinger/RenderEngine/gl/GLES20RenderEngine.h
+++ b/services/surfaceflinger/RenderEngine/gl/GLES20RenderEngine.h
@@ -48,14 +48,24 @@
     std::unique_ptr<Image> createImage() override;
 
     void primeCache() const override;
-
-    bool isCurrent() const;
+    bool isCurrent() const override;
     bool setCurrentSurface(const Surface& surface) override;
     void resetCurrentSurface() override;
-
+    base::unique_fd flush() override;
+    bool finish() override;
+    bool waitFence(base::unique_fd fenceFd) override;
+    void clearWithColor(float red, float green, float blue, float alpha) override;
+    void fillRegionWithColor(const Region& region, uint32_t height, float red, float green,
+                                     float blue, float alpha) override;
+    void setScissor(uint32_t left, uint32_t bottom, uint32_t right, uint32_t top) override;
+    void disableScissor() override;
+    void genTextures(size_t count, uint32_t* names) override;
+    void deleteTextures(size_t count, uint32_t const* names) override;
     void bindExternalTextureImage(uint32_t texName, const Image& image) override;
+    void readPixels(size_t l, size_t b, size_t w, size_t h, uint32_t* pixels) override;
     status_t bindFrameBuffer(Framebuffer* framebuffer) override;
     void unbindFrameBuffer(Framebuffer* framebuffer) override;
+    void checkErrors() const override;
 
 protected:
     void dump(String8& result) override;