Auto merge of #133476 - SomeoneToIgnore:stable, r=BoxyUwU,davidbarsky

[stable(not yet) backport] Revert r-a completions breakage

This PR revers recent completion-related changes in r-a, which caused nvim and helix to malfunction.
Changes reverted:
1. https://github.com/rust-lang/rust-analyzer/pull/18167
2. https://github.com/rust-lang/rust-analyzer/pull/18247
3. https://github.com/rust-lang/rust-analyzer/pull/18503

See https://github.com/rust-lang/rust-analyzer/pull/18503#issuecomment-2498920382 for more context

cc `@BoxyUwU`