nir,rusticl/mem: fix gl sharing for buffer objects

This fixes three bugs in our gl_sharing implementation:

1. nir_lower_cl_images not setting info.image_buffers.
2. the size for buffer objects were set to 0 failing almost any operation on them
3. we didn't support GL_TEXTURE_BUFFER as the CL CTS test was buggy (https://github.com/KhronosGroup/OpenCL-CTS/pull/1885) and I haven't checked why it was crashing as I just though "ah.. that's just freeglut".

Closes: #10505 (closed)