Reuse machinery from tail_expr_drop_order for if_let_rescope

[compiler-errors]

Namely, it defines its own extract_component_with_significant_dtor which is a bit more accurate than Ty::has_significant_drop, since it has a hard-coded list of types from the ecosystem which are opted out of the lint.¹

Also, since we extract the dtors themselves, adopt the same label we use in tail_expr_drop_order to point out the destructor impl. This makes it much clear what's actually being dropped, so it should be clearer to know when it's a false positive.

This conflicts with #137444, but I will rebase whichever lands first.

Footnotes

1. Side-note, it's kinda a shame that now there are two functions that presumably do the same thing. But this isn't my circus, nor are these my monkeys. ↩

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[rustbot]

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

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Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

[bors]

☔ The latest upstream changes (presumably #137497) made this pull request unmergeable. Please resolve the merge conflicts.

[bors]

☔ The latest upstream changes (presumably #137608) made this pull request unmergeable. Please resolve the merge conflicts.