Auto merge of #154304 - zetanumbers:typeck_root, r=petrochenkov

Make typeck a tcx method which calls typeck_root query



Currently typeck query itself calls `tcx.typeck(tcx.typeck_root_def_id(key))` if its key isn't a type-check root. I thought this might be an overhead and made typeck a tcx method which calls typeck_root query instead.

This is a step to simplify `cache_on_disk_if` query modifier.

@petrochenkov please run perf