Make framebuffer DEPTH_STENCIL works well + StencilTexture higher priority.

Make framebuffer DEPTH_STENCIL works well + StencilTexture higher priority.

Framebuffer cannot attach both Depth and Stencil
at indivisual Renderbuffer.

So, If FrameBuffer::Attachment::Mask::DEPTH_STENCIL used, result is broken.

This patch make if framebuffer try to use both Depth and Stencil,
let Framebuffer use GL_DEPTH_STENCIL_ATTACHMENT.

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Make stencilTexture has higher proirity than depthTexture in gles case.

Current dali API only have AttachDepthTexture and
AttachDepthStencilTexture.
And, AttachDepthStencilTexture input texture stored in createInfor's
stencilTexture level.

Current device didn't support to seperate each depth/stencil result in gles.
So we need to assume that stencilTexture is depth_stencil texture.

Change-Id: I2a6f46b66c1ef64a6f54e6cc4fc934f0ad276406
Signed-off-by: Eunki, Hong <eunkiki.hong@samsung.com>