(#21416) Allow file_line to match multiple lines

Without this commit the file_line type will outright fail if multiple
lines match the given regex. This commit allows the file_line type and
provider to optionally match and modify all matching lines.

Changeset rebased into a single commit by Adrien Thebo <adrien@puppetlabs.com>
Merge branch 'pull-163'

This closes GH-163