dsymbolsem/InstMemberWalker: also visit generated structs' members

[yanok]

While updating children's minst only going over members is not enough: structs may also have generated methods that are not in members.

As a result, if a generated method instantiates a template, it gets a poentially wrong minst, so can be omitted from the compilation result.

Fixes Bugzilla Issue 24830

[dlang-bot]

Thanks for your pull request and interest in making D better, @yanok! 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
✓	24830	normal	separate compilation + circular deps + templated opCmp = missing symbols

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#17022"