[declaration.d] move checkDisabled and expandInitializer to expre…

[thewilsonator]

…ssionsem.d

[dlang-bot]

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

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#16941"

[dkorpel]

Considering the functions act on declarations and not expressions, why expressionsem and not dsymbolsem?

[thewilsonator]

There are no uses in dsymbolsem.d.
There is a single use in funcsem.d that should be removed very soon for the deprecation period for the removal of the delete keyword https://github.com/dlang/dmd/blob/master/compiler/src/dmd/funcsem.d#L1652

There are 8 uses in expressionsem.d and 3 in typesem.d, so I went with expressionsem.d.