Fix Issue 17870 - Can't alias a mix of parent and child class members

[12345swordy]

Reboot of the PR #11633
Addressed @wilzbach test requirements

cc @RazvanN7

[dlang-bot]

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	17870	normal	Can't alias a mix of parent and child class members

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#13380"

[RazvanN7]

Thanks @12345swordy for following through with this!

As a side note, you can push directly to an open PR to not go through the hurdle of opening a new one: https://ardupilot.org/dev/docs/editing-prs.html