char predicates using libmojibake

see issue #5939 

Please note from string.jl the following:
```
include("utf8proc.jl")
importall .UTF8proc
```

The include was needed to resolve a bootstrap related error.  Is there a preferred means of dealing with this type of issue?
Maybe use an explicit loop rather than `all`.  These are probably not performance critical, but writing out a loop is not too much of a sacrifice for a little more performance here.