prepare for fix of issue 20138 ("is expression not evaluating correct…

[aG0aep6G]

…ly?")

With issue 20138 fixed, const U and shared U do match const shared T,
and they leave the other qualifier intact. So const shared U must be
attempted first if we want to strip both qualifiers.

This is blocking dlang/dmd#10317.

[dlang-bot]

Thanks for your pull request and interest in making D better, @aG0aep6G! 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:)

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✗	20138	blocker	is expression not evaluating correctly?

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 + phobos#7147"

[TurkeyMan]

This is very strange... I don't understand, but I take your word for it :)

[thewilsonator]

Please make sure this effect is highlighted in a changelog for dlang/dmd#10317