[Issue 24330] Redundant template instantiations for equal string/array literals

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24330

--- Comment #1 from Dennis <dkorpel at live.nl> ---
Related issue:

```D
void f(int[] b)() { }

void main()
{
    enum dstring s = (""d ~ cast(dchar) 0xFFFF_FFFF);
    f!(cast(int[]) s ~ []); // works
    f!(cast(int[]) s); // invalid UCS-32 char \Uffffffff
}
```

Fails because it tries to mangle the int[] as a string because it's a
StringExp.

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