tools: check-imports.py false negatives

[bnoordhuis]

Refs: #29222

As that PR shows, there are some unused imports that tools/check-imports.py doesn't catch because:

1. They're used in comments.
2. The tool doesn't match at word boundaries (e.g. FromJust is considered a use of Just.)

[ayushmandey97]

Hey, I'm a bit new to opensource. Have some experience with Python and regex, and this looks interesting. Can I take this up?

[sam-github]

@ayushmandey97 Yes, you are welcome to, thanks.

[ayushmandey97]

I'll be adding support for multi-line comments as well.

There's one issue though, I added a dummy 'using' statement in one of the .cc files to check if an error was thrown, but the check-imports.py file ran without any log statements.
Any suggestions on how to test it in-case that's a wrong approach?

Another thing, since this is my first PR for Node, please feel free to let me know if I've made mistakes in the process or the code itself.

[ayushmandey97]

@sam-github the checks have been implemented. Please review once and let me know if any changes are required.

@bnoordhuis please have a look at the PR.