[clang-tools-extra] [clang-tidy][NFC] Add `.editorconfig` for `.rst` files (PR #167269)

[via cfe-commits]

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+[clang-tidy/checks/**/*.rst]
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zeyi2 wrote:

> Instead of this path, could we just place it in `clang-tool-extra/docs/clang-tidy/checks/`? Will it work like that?

Also, should we apply these checks to `list.rst`? The 80 chars limitation may require a lot of refactoring for this file.

https://github.com/llvm/llvm-project/pull/167269