[clang-tools-extra] [clang-tidy] Add readability-string-view-substr check (PR #120055)

[via cfe-commits]

github-actions[bot] wrote:

<!--LLVM CODE LINT COMMENT: doc8-->


:warning: RST documentation linter, doc8 found issues in your code. :warning:

<details>
<summary>
You can test this locally with the following command:
</summary>

```bash
doc8 -q clang-tools-extra/docs/clang-tidy/checks/readability/stringview-substr.rst clang-tools-extra/docs/clang-tidy/checks/list.rst --config clang-tools-extra/clang-tidy/doc8.ini
```

</details>

<details>
<summary>
View the output from doc8 here.
</summary>

```
clang-tools-extra/docs/clang-tidy/checks/readability/stringview-substr.rst:6: D001 Line too long
clang-tools-extra/docs/clang-tidy/checks/readability/stringview-substr.rst:11: D001 Line too long
clang-tools-extra/docs/clang-tidy/checks/readability/stringview-substr.rst:13: D001 Line too long
clang-tools-extra/docs/clang-tidy/checks/readability/stringview-substr.rst:18: D001 Line too long
clang-tools-extra/docs/clang-tidy/checks/readability/stringview-substr.rst:19: D001 Line too long
```


Note: documentation lines should be less than 80 characters wide.
</details>


https://github.com/llvm/llvm-project/pull/120055