Since GL has no notion of texture formats that can be used for different
types of textures, merge the TextureFormatCaps texture support members.

Also merge the various renderability members since the texture type is
enough to determine what type of renderable a format is.

BUG=angle:658

Change-Id: I7cba50b147fcca8f3880d65c06c57df9c65ed19c
Reviewed-on: https://chromium-review.googlesource.com/206830Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>