test(rome_js_formatter): support report prettier metric as a json file

[IWANABETHATGUY]

Summary

part of #2555
To achieve printing diff between main branch and pull request branch, a few steps we need to do list below

1. save prettier compatibility metric on main branch
2. switch to pull request branch
3. save prettier compatibility metric on pull request branch
4. compare two metrics and echo the diff.

Obviously, Markdown is not a good format for comparing, so we need to add an extra format to save metrics, which is Json
just like Parser conformance

This pull request introduces these two changes:

1. Add an option to report the prettier compatibility metric in json or markdown format.
2. Support choosing file_name to save.

Test Plan

No need to test

[ematipico]

Could you add few lines in the description of the PR about:

• why you're adding this to the tests and what kind of problem we're trying to solve;
• a reference to an issue where this new addition was discussed;

[IWANABETHATGUY]

Done

[yassere]

Thanks for working on this! I agree that it makes sense to have a json option so that changes can be compared more easily in CI.

Currently, this PR duplicates a lot of the report calculations, which makes it more likely to fall out of sync if we modify our metrics in the future. Could you extract those calculations so that the report_json and report_markdown methods are only directly responsible for the differences that are specific to that report type?

Maybe there could be a method that produces a PrettierReport that the individual report_X methods know how to print into different formats?

[IWANABETHATGUY]

agree

[yassere]

We could also update the .gitignore to ignore crates/rome_js_formatter/report.* rather than just the markdown file.

[MichaReiser]

Agree with Yasser. I think it would be good to factor out the computation into a helper function that returns the numbers and the markdown/json functions only print the results differently.

[IWANABETHATGUY]

I have refactored the code, I think I am ready for reviewing.

[MichaReiser]

Thanks for doing the refactor. That should help us to keep the implementations in sync in the future.

I've a small comment that may help to reduce some code. Let me know if you want to address it before merging or prefer to keep it as is.