The stripping of trailing spaces currently happens as part of
`git_attr_fnmatch__parse`. As we aren't currently parsing
trailing whitespaces correct in case they're escaped, we'll have
to change that code, though. To make actual behavioural change
easier to review, refactor the code up-front by pulling it out
into its own function that is expected to retain the exact same
functionality as before. Like this, the fix will be trivial to
apply.