Linter plugins: Add `cwd` property to `Context`

[overlookmotel]

As described in ESLint's docs: https://eslint.org/docs/latest/extend/custom-rules#the-context-object

The absence of this property was mentioned in #14649 (comment) as a blocker to supporting eslint-plugin-better-tailwindcss plugin.

I'm not sure exactly what cwd means in this context - I'm guessing it's probably not the same as process.cwd(), and more likely to be the highest directory which Oxlint has been asked to lint files in. We'd need to check what ESLint does here and replicate it.