Fix StringName comparison

[AThousandShips]

Comparisons were not correct, probably due to being cast to String and compared there (due to the casting not being explicit) but not clear how it was broken, but now it isn't

Now:

a == b false
a != b true
a <  b false
a <= b false
a >  b true
a >= b true

Fixes: #76218

Documentation handled by #77083

The alternative to this would be to change how the comparison is made by changing how it works in variant ops, but I think this is more elegant and doesn't break compat (for the non-broken comparisons), alternatively we could just remove the other comparisons

I feel keeping the pointer based comparisons is useful, doesn't add a lot of hacky fixes to avoid using the built-in operators on StringName (and the lack of any such method of comparison indicates to me that the pointer-based comparison was intended), and if you want unicode comparisons you can just cast it to String

[RandomShaper]

Should be merged with #77083.

[YuriSizov]

Thanks!

[AThousandShips]

Thank you!

[YuriSizov]

Cherry-picked for 4.0.4.