Add `get_line` confusable to `Stdin::read_line()`
This pull request resolves https://github.com/rust-lang/rust/issues/131091
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I've updated tests for `tests/ui/attributes/rustc_confusables_std_cases` in order to verify this change is working as intended.
Before I submitted this pull request, I had a pull request to my local fork. If you're interested in seeing the conversation on that PR, go to https://github.com/JakenHerman/rust/pull/1.
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**Testing**:
Run `./x.py test tests/ui/attributes/rustc_confusables_std_cases.rs`
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