st/mesa: fix texture array dimensions

st/mesa: fix texture array dimensions

For 1D/2D texture arrays use the pipe_resource::array_size field.
In OpenGL 1D arrays texture use the height dimension as the array
size and 2D array textures use the depth dimension as the array size.
Gallium uses a special array_size field instead.  When setting up
gallium textures or comparing Mesa textures to gallium textures we
need to be extra careful that we're comparing the right fields.

The new st_gl_texture_dims_to_pipe_dims() function maps OpenGL
texture dimensions to gallium texture dimensions and simplifies
this quite a bit.