This fixes the scenario when EGLImage source and target have different types.
For example, a texture is created with unsigned format using glTexImage2D,
it is used as a source of EGLImage with eglCreateImageKHR,
and then the EGLImage is used to create a renderbuffer target with
glEGLImageTargetRenderbufferStorageOES.

OES_EGL_image doesn't specify what should happen in this case,
but GL implementations (Nexus 5X) seem to allow using this renderbuffer in
glFramebufferRenderbuffer and the resulting framebuffer is complete.
Thus, in this case, instead of checking whether the renderbuffer format
can be used in glFramebufferRenderbuffer, we need to check whether the
original texture can be used in glFramebufferTexture2D.
Similarly in reverse direction.

Also, for the case of source renderbuffer and target texture,
presume that glEGLImageTargetTexture2DOES will succeed regardless of
renderbuffer format.

1. Add isRenderable and isTexturable checks to egl::Image class,
   and perform different checks depending on source type.
2. Add isRenderable check to FramebufferAttachment and delegate EGLImage
   attachments check to egl::Image.
3. Use these checks in validation of EGLImageTargetTexture2D,
   EGLImageTargetRenderbufferStorage and when checking attachment completeness

Bug: angleproject:2567

Change-Id: I8e9f4a2930a4075a4d8464f62582c6825270187e
Reviewed-on: https://chromium-review.googlesource.com/1192585
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>