isl_pw_*_align_params: reuse isl_pw_*_get_domain_space
isl_pw_*_align_params: reuse isl_pw_*_get_domain_space

This reduces the dependence on the internal representation.

Note that isl_parameter_alignment_reordering now gets passed
the space of the domain rather than the full space,
but isl_parameter_alignment_reordering currently only uses
the parameters of this space.

Signed-off-by: Sven Verdoolaege <dd860110a62b19214c4ee03aec0abffecb4e86b8@cerebras.net>

Meinersbur/isl,Meinersbur/isl,Meinersbur/isl,Meinersbur/isl