Enhancement: Add `backup` options `--files-from-{verbatim,raw}`

The new `backup` options `--files-from-verbatim` and `--files-from-raw` read a
list of files to back up from a file. Unlike the existing `--files-from`
option, these options do not interpret the listed filenames as glob patterns;
instead, whitespace in filenames is preserved as-is and no pattern expansion is
done. Please see the documentation for specifics.

These new options are highly recommended over `--files-from`, when using a
script to generate the list of files to back up.

https://github.com/restic/restic/issues/2944
https://github.com/restic/restic/issues/3013
