mesa: allow mutable buffer textures to back GL ES images
mesa: allow mutable buffer textures to back GL ES images

Since there is no way to create immutable texture buffers in GL ES,
mutable buffer textures are allowed to back images. See issue 7 of the
GL_OES_texture_buffer specification.

Signed-off-by: Ilia Mirkin <bcbbb7aa705ec3a5fc5824c01a845186c3d62fca@alum.mit.edu>
Reviewed-by: Samuel Pitoiset <506e97eed81d9e59d22f4c73fb51123bb62b4a30@gmail.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler