PATCH: [perl #121778]:BBC KAMIPO/autobox-String-Inflector

PATCH: [perl #121778]:BBC KAMIPO/autobox-String-Inflector

When I wrote commit 645de4ceb9a7cbcff21ef7df3a5f5eb36259571e,
and its predecessor commit, I wrongly thought that this code used a
count of bytes rather than characters.  I no longer remember why.
My previous experience was that a lot of code in the regex system talked
about characters in the documentation, when in fact bytes were what was
really meant.  The comments had never been properly updated to account
for UTF-8

But this code in fact is supposed to use a character count, and this
commit changes it to do so.