[RenderEngine] Make BindNativeBufferAsFramebuffer more generic.

BindNativeBufferAsFramebuffer is a helper class that manages resource of an EGL
image for screenshot capturing. However, as a public API it ties to GLES. This
patch abstracts framebuffer out as Framebuffer and uses it instead of EGL
image. As a result, we can move the most of the implementation of
bindNativeBufferAsFrameBuffer and unbindNativeBufferAsFrameBuffer to
GLFramebuffer so that it manages its own resources, and move the rest of the
implementation to GLES20RenderEngine and get rid off two virtual functions.

Minor: Clean up some coding style.

BUG: 112585051
Test: Build, flash, boot and run some display validation
Change-Id: I787625089f8959cc273d4756baa7135cb004ed2d