Add support for linting ECR files

[nobodywasishere]

This should be a simple process of checking if the filename ends with .ecr, then calling ECR.process_file or ECR.process_string (with a clean rescue in case an error occurs), and running the linter over the outputted code.

[nobodywasishere]

Only major issues would be Lint/UselessAssign, as there may be other .ecr files rendered within the current scope later. That's one downside of ECR in comparison to Jinja, where ECR files are just expanded into the current scope instead of having their own that vars are passed into. If this was merged, it'd probably be worth it to turn off that rule for ECR files.

[nobodywasishere]

Prototype branch here: https://github.com/nobodywasishere/ameba/tree/nobody/ecr-lint

Combined with linting while typing, this makes writing ECR a significantly better experience.

[Sija]

That sounds like a helpful feature to have ❤️
One thing I'm not really fond of is monkey-patching ECR lexer, although I do understand it's needed for this to work.
Perhaps we could wait with the integration until the required changes make their way into the upstream.

[nobodywasishere]

That was my plan, started working on a PR for this last night. Monkey patch was just a hack to showcase proof of concept.

[Sija]

Unblocked by crystal-lang/crystal#15222