Provide a nice error message when trying to compare two Str

[Anton-4]

NOTE: do not implement this in the old rust compiler, only in the new zig compiler (see src folder) when it is far enough along.

"abc" < "def"

currently results in:

This 1st argument to > has an unexpected type:

4│ "abc" > "dev"
^^^^^
The argument is a string of type:
Str
But > needs its 1st argument to be:
Num a

It's hard to figure out for the user how they can implement their desired behavior.
We should intercept this particular type error and add a nice message with a link to "Why does Roc not handle strings like most languages?" in the faq.