GL_APPLE_texture_format_BGRA8888 is similar to
GL_EXT_texture_format_BGRA8888 but explicitly mentions texture storage
support for OpenGL ES 3.0. It adds the format as texture-only (i.e.
non-renderable), but GL_EXT_texture_format_BGRA8888 makes it color-
renderable.

Also allow a sized internalformat of GL_BGRA8_EXT. Previously we were
only allowing unsized internalformat GL_BGRA.

Change-Id: Ieb3a4f85847035392445d0a924591f5531e424d9
Reviewed-on: https://swiftshader-review.googlesource.com/16069Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>