Add project-specific lints with ast-grep (#5637)
ast-grep[0] is a tool that uses tree-sitter[1] and a pattern language to
match against code using its ast. It implements code transformation,
querying, and linting.
Since clippy isn't extensible for project-specific lints, this adds a
first ast-grep lint disallowing `context` as a variable name. Currently
it's set to warning as usage is addressed.
To run, install ast-grep, then run `ast-grep scan`. Example output:
```
warning[no-context]: Don't name variables `context`.
┌─ ./crates/turbopack-ecmascript-hmr-protocol/src/lib.rs:132:9
│
132 │ pub context: &'a str,
│ ----^^^^^^^---------
│
= Use a more specific name, such as chunking_context, asset_context, etc.
```
[0] https://ast-grep.github.io
[1] https://tree-sitter.github.io/tree-sitter/
