mesa: modify _mesa_copy_linked_program_data() to take gl_linked_shader

mesa: modify _mesa_copy_linked_program_data() to take gl_linked_shader

This allows us to do some small tidy ups, but will also allow us to call
a new function that copies values to a shared shader info from here.

In order to make this change this function now requires
_mesa_reference_program() to have previously been called.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>