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Auto merge of #127421 - cjgillot:cache-iter, r=fmease
Cache hir_owner_nodes in ParentHirIterator.
Lint level computation may traverse deep HIR trees using that iterator. This calls `hir_owner_nodes` many times for the same HIR owner, which is wasterful.
This PR caches the value to allow a more efficient iteration scheme.
r? ghost for perf
