MINOR: tools: add support for ist to the word fingerprinting functions

MINOR: tools: add support for ist to the word fingerprinting functions

The word fingerprinting functions are used to compare similar words to
suggest a correctly spelled one that looks like what the user proposed.
Currently the functions only support const char*, but there's no reason
for this, and it would be convenient to support substrings extracted
from random pieces of configurations. Here we're adding new variants
"_with_len" that take these ISTs and which are in fact a slight change
of the original ones that the old ones now rely on.