feat: add no-missing-link-fragments rule

[SwetaTanwar]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request?

This PR adds a new rule no-missing-link-fragments to ensure there is no missing link fragment in the markdown

What changes did you make? (Give an overview)

Added the no-missing-link-fragments rule, along with documentation and tests.

Related Issues

fixes #369

Is there anything you'd like reviewers to focus on?

[snitin315]

Thank you for taking this up. This looks like a good start. I have added a few suggestions on documentation & few false postives. I think there are few more cases we should cover that MD051 handles as well:

1. HTML ids:

   <a id="bookmark"></a>
   
   [Link](#bookmark) // valid

2. #top: HTML links to #top scroll to the top of a document.

   [Link](#top)

3. Custom fragment syntax used by GitHub to highlight specific content in a document.

   [Link](#L20) // Valid
   
   [Link](#L19C5-L21C11) // Valid

[nzakas]

LGTM. Would like @lumirlumir to review before merging.

[snitin315]

LGTM, thanks!

[SwetaTanwar]

@lumirlumir Can you please review the PR

[nzakas]

@lumirlumir please re-review this when you can.

[lumirlumir]

@nzakas Sure, but I think my reviews haven’t been addressed yet. It seems like a bit more time might be needed.

@SwetaTanwar If you don’t mind, and if you’re still working on it, could you mark this PR as a draft while you continue making progress?

[lumirlumir]

Could you take a look at the CI failure? Please ping me when the ongoing tasks are done :)

[SwetaTanwar]

@lumirlumir The checks are passing now, fixed the CI failure due to Duplicate identifier 'MarkdownNode.

Also, I have addressed all the feedbacks you gave above

[lumirlumir]

LGTM. Would like @snitin315 and @nzakas to verify the changes before merging.

[snitin315]

LGTM. Nice job, and thanks for being so patient with all the back and forth.