fix 24745 - improve associative array syntax error message

[royalpinto007]

No description provided.

[dlang-bot]

Thanks for your pull request and interest in making D better, @royalpinto007! 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.

---

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

Auto-close	Bugzilla	Severity	Description
✓	24745	enhancement	Better error message when creating an associative array with the wrong syntax

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 "stable + dmd#16832"

[ryuukk]

why 6 lines of error messages? it should only be 1 line

[ntrel]

1. I think the new message should only be shown when detecting a colon after a non-identifier expression. E.g. it looks like the message would show for {expr expr}, which is unlikely to be intended as an array initializer.
2. The message could say (associative) array, because array literals can have indexes too.

Edit: And (1) is why fail_compilation/fix350a.d and fail_compilation/fix350b.d are failing.