60982dc8fc
feat: Support multiple tab stops for completions in VSCode
Uses the native VSCode support for `SnippetTextEdit`s. Fixes #13229 and fixes #8531.
https://github.com/rust-lang/rust-analyzer/assets/13354275/a2d2c033-bb30-4f34-92ca-bf3f4f744cdc
This is done in a slightly hacky way, as `vscode-languageclient` can't convert RA's `SnippetTextEdit`s into vscode `SnippetTextEdit`s and will appear to use a [different format](295aaa393f/types/src/main.ts (L1501-L1516)) in the future.
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~~Marked as draft since as-is, this will cause completions to double-indent any multi-line code generated.~~
**Update:** This also fixes up edits so that any multi-line code won't be double-indented.