mesa,meta: move gl_texture_object::TargetIndex initializations

mesa,meta: move gl_texture_object::TargetIndex initializations

Before, we were unconditionally assigning the TargetIndex field in
_mesa_BindTexture(), even if it was already set properly.  Now we
initialize TargetIndex wherever we initialize the Target field, in
_mesa_initialize_texture_object(), finish_texture_init(), etc.

v2: also update the meta_copy_image code.  In make_view() the
view_tex_obj->Target field was set, but not the TargetIndex field.
Also, remove a second, redundant assignment to view_tex_obj->Target.
Add sanity check assertions too.

Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>
Tested-by: Mark Janes <mark.a.janes@intel.com>