Accept AbstractChar in count and findall (::Char, ::String) (#38675)
This change solves an issue raised in this post, in which searching for a char in a string results in a Method error: https://discourse.julialang.org/t/method-for-counting-characters-in-string-count-a-batman-vs-count-a-batman/51153
Co-authored-by: Stefan Karpinski <stefan@karpinski.org>
Co-authored-by: Steven G. Johnson <stevenj@mit.edu>