nir: Use getters for nir_src::parent_*

nir: Use getters for nir_src::parent_*

First, we need to give the parent_instr field a unique name to be able to
replace with a helper.  We have parent_instr fields for both nir_src and
nir_def, so let's rename nir_src::parent_instr in preparation for rework.

This was done with a combination of sed and manual fix-ups.

Then we use semantic patches plus manual fixups:

    @@
    expression s;
    @@

    -s->renamed_parent_instr
    +nir_src_parent_instr(s)

    @@
    expression s;
    @@

    -s.renamed_parent_instr
    +nir_src_parent_instr(&s)

    @@
    expression s;
    @@

    -s->parent_if
    +nir_src_parent_if(s)

    @@
    expression s;
    @@

    -s.renamed_parent_if
    +nir_src_parent_if(&s)

    @@
    expression s;
    @@

    -s->is_if
    +nir_src_is_if(s)

    @@
    expression s;
    @@

    -s.is_if
    +nir_src_is_if(&s)

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Acked-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24671>