Fix Issue 21481 - functions in overloaded template are lost when the …

[BorisCarvajal]

…template overloads an alias

[dlang-bot]

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	21481	normal	functions in overloaded template are lost when the template overloads an alias

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#12092"

[thewilsonator]

This should be a compilable test

[BorisCarvajal]

Same as #12091

There are already a few compile-time tests in this file, the cost of adding it here is 0ms vs creating another.
Unfortunately there's no test/compilable/overload.d 😞 .