Move semantic methods out of expression.d

[RazvanN7]

Trying to remove semantic dependencies from expression.d. Next step is to create a visitor toBoolean methods and after that, hopefully, we can get rid of the expressionsem and dsymbolsem dependencies.

[dlang-bot]

Thanks for your pull request and interest in making D better, @RazvanN7! 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 annotated coverage diff directly on GitHub with CodeCov's browser extension
• 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 fetch digger
dub run digger -- build "master + dmd#8479"

[WalterBright]

Trying to remove semantic dependencies from expression.d.

Rationale?

[RazvanN7]

@WalterBright Trying to pull out semantic methods out of AST nodes so that we can have a separation between parsing and semantic analysis. This will enable to replace the massive duplication in ASTBase with simple imports of AST nodes.