Implementation of diagnostic reporting style for dfa engine

[Iskaban10]

Diagnostic reporting mechanism. Can be used with -verror-style = diagreport. Code taken from here.
Example output:

Previous PR became messy. Hence made another PR.

[dlang-bot]

Thanks for your pull request and interest in making D better, @Iskaban10! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.
Please verify that your PR follows this checklist:

• My PR is fully covered with tests (you can see the coverage diff by visiting the details link of the codecov check)
• My PR is as minimal as possible (smaller, focused PRs are easier to review than big ones)
• I have provided a detailed rationale explaining my changes
• New or modified functions have Ddoc comments (with Params: and Returns:)

Please see CONTRIBUTING.md for more information.

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If you have addressed all reviews or aren't sure how to proceed, don't hesitate to ping us with a simple comment.

Bugzilla references

Your PR doesn't reference any Bugzilla issue.

If your PR contains non-trivial changes, please reference a Bugzilla issue or create a manual changelog.

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#23124"

[dkorpel]

Can you please force push a new branch instead of opening new PRs? That prevents review comments getting erased.

[dkorpel]

#23115 (review)

[Iskaban10]

Can you please force push a new branch instead of opening new PRs? That prevents review comments getting erased.

Was facing some issue in re-opening the previous PR. I was not very familiar with managing git histories.
Closing this PR because I have been able to re-open the original PR.