[FEATURE REQUEST] access pillar dunder in extension modules during pillar render

[dwoz]

Historically the pillar dunder has never been available or worked in extension modules during pillar render, due to what I can only assume is a bug/oversight in the overly-complex mess of branches and logic in the pillar rendering code. Functionally there is very little reason this shouldn't work, and it even appears like it may have worked at some point, or at least was intended to work by the fact that the ext_pillar data was stuffed right back into opts before attempting to render the remainder of the pillar.

The missing piece to the puzzle here was that the partially-rendered ext_pillar data wasn't available in the opts dict packed into the salt.loader.minion_mods() call when it was generated, and the fact that the functions weren't reloaded after the pillar dict was updated. This commit fixes both of those things.

Ensure the minion_mods are always reloaded with the updated opts dict containing the partial pillar data when rendering pillar with ext_pillar_first enabled.

From #63398