function signature for the "^" operator for strings

[udohjeremiah]

The returned value of this function should be shown so as to clear ambiguities on some scenarios.

As an example, it doesn't matter if the string is of length 0 or 1, the returned value will always be a string. This isn't intuitive to think of as first glance:

julia> 'a' ^ 1
"a"

julia> 'a' ^ 0
""

Since it's said no where for the function to always return a string, its best to be in the function signature. And this will clear the ambiguities as pointed above.

A great example of this is in the * operator for strings and regex:

help?> *

  *(s::Union{AbstractString, AbstractChar}, t::Union{AbstractString, AbstractChar}...) -> AbstractString

  *(s::Regex, t::Union{Regex,AbstractString,AbstractChar}) -> Regex
  *(s::Union{Regex,AbstractString,AbstractChar}, t::Regex) -> Regex

As seen above, the ^ operator should follow the same standard too!

I opened #46885 on the regex part as well, so its balanced.

[fredrikekre]

I opened #46885 on the regex part as well, so its balanced.

It would be preferable to group multiple changes like this in the same PR (to save CI resources, and reviewer resources).