Auto merge of #39309 - eddyb:map-shmap, r=nikomatsakis
Rename tcx.map to the far more descriptive tcx.hir.
Also a bit more renaming because `ast_map` and `'ast` were still used with HIR.
Main motivation is to "free up" `tcx.map`, or rather, `tcx.maps`, to consolidate `ty::maps` there.
r? @nikomatsakis