Fix #20601 - hasIndirections does not handle static arrays of length 0 correctly

[jmdavis]

hasIndirections doesn't handle static arrays of length 0 correctly (they don't actually have any indirections), because operator precedence resulted in the check for 0 length static arrays having no actual effect.

I also copied the test for
https://issues.dlang.org/show_bug.cgi?id=12000 from std.traits to here, because it's really a compiler bug that's being tested rather than hasIndirections itself (so being in the compiler repo arguably makes more sense), and it also arguably makes more sense to put it next to the actual implementation than in std.traits where it's been.

[dlang-bot]

Thanks for your pull request, @jmdavis!

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