[why]
We can limit the font files to patch with the gotta-patch-em-all script
to some specific file names; the case insensitive beginning of the
basename of the font file, to be specific.

Sometimes we do not know how the actual font files are named, we just
know the directory name.

[how]
The old filter checked for the beginning of a file name, so we keep this
behavior and allow to check for the beginning of a directory name.

As differentiator the first character of the passed filter is used. As a
slash is not allowed in the file name filters: If the first char is a
slash, we search for font files in a directory that begins with that
name. The file name is not considered in this case.

Examples:

gotta-patch-em-all-font-patcher!.sh Fira

  Patches all font files that begin (case insensitive) with 'fira'.
  It must be the basename of the font file, the path to the file is not
  considered. (Old behavior.)
  Translated to a glob this is roughly **/Fira*.[ot]tf

gotta-patch-em-all-font-patcher!.sh /Fira

  Patches all font files that are in directories that begin (case
  insensitive) with 'fira'. It can not be the beginning of the font
  file basename.
  Translated to a glob this is roughly **/Fira*/**/*.[ot]tf

Signed-off-by: Fini Jastrow <ulf.fini.jastrow@desy.de>

[why]
The font matix contains the directory names of the font files. The
directory names are taken from
  bin/scripts/lib/fonts.json
and specifically extracted with
  bin/scripts/get-font-names-from-json.sho

That script returns the .folderNames

Later in the release script we use the folder name to limit the fonts
that patch-em-all shall process. Unfortunately patch-em-all could (until
the previous commit) just work with font-filenames and not with
directory names. But the matrix gives us just directory names.

This is for example a problem with this fonts:
$ ll src/unpatched-fonts/BigBlueTerminal
-rw-rw-r-- 1 fini fini 25632 Jan  1 14:03 BigBlue_Terminal_437TT.TTF
-rw-rw-r-- 1 fini fini 69964 Jan  1 14:03 BigBlue_TerminalPlus.TTF

The *directory* of that fonts is correctly noted in fonts.json as
"BigBlueTerminal" but the font files do not begin with that!

[how]
Now, that patch-em-all can also filter on the directory name, we just
need to utilized that in the workflow run. If the filter shall work on
directory names the first character needs to be a slash, so we just
prepend it to name we got from the matix.

Fixes: #824

Signed-off-by: Fini Jastrow <ulf.fini.jastrow@desy.de>