Auto merge of rust-lang#33296 - jseyfried:non_idempotent_lowering, r=nrc

Remove the requirement that ast->hir lowering be reproducible

This PR changes the ast->hir lowerer to be non-reproducible, and it removes the lowering context's id cache.

If the `hir` of an `ast` node needs to be reproduced, we can use the hir map instead of the lowerer -- for example, `tcx.map.expect_expr(expr.id)` instead of `lower_expr(lcx, expr)`.

r? @nrc

Author: bors