Fix getSymbolsByUDA by replacing broad __traits(compiles) with a more narrow condition

[RazvanN7]

This was discovered in dlang/dmd#14554.

hasUDA uses getUDAs underneath which in turn uses traits(getAttributes). Up until dmd PR 14554 getUDAs would happily accept an overload set and because of the bug in __traits(getAttributes) it would just check the first lexicographically overload encountered.

getSymbolsByUDA which uses hasUDA internally would first check if hasUDA is callalble on the members of the passed aggregate by using __traits(compiles, hasUDA!member). This was done to prevent calling traits(getAttributes) on types or alias sequences, however, with the new deprecation from dmd PR 14554 and since phobos compiles with -de the __traits(compiles) check now fails for functions that have overloads, thus breaking getSymbolsByUDA.

The fix is to narrow the condition by specifically checking for types and alias sequences in the internals of getSymbolsByUDA, which this PR does, thus unblocking dmd PR 14554.

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Testing this PR locally

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dub run digger -- build "master + phobos#8631"

[RazvanN7]

cc @dkorpel

[Geod24]

You know, enum isAliasSeq = (Args.length != 1) works too ;)

[quickfur]

This change unfortunately caused a regression: https://issues.dlang.org/show_bug.cgi?id=23776

[JohanEngelen]

Possibly introduced another regression: https://issues.dlang.org/show_bug.cgi?id=23977