font-patcher: Incorporate FontnameParser

[why]
A lot people expect the font-patcher to be a stand alone script. They
even think that the source glyphs (symbols) to be added to be somehow
magically there and one PR makes sure that they are fetched if missing.

The same problem arises when we have a script distributed over multiple
files. For maintenance reasons and code quality this is what one wants.
But that might hinder easy use of the font-patcher.

[how]
Put all the code in the main script.

That has an additional drawback: For the nameparser_test* scripts to
work we need stand alone files for that classes. Now the code is
duplicated and will get out of sync.

I have no solution for that, and it all boils down what Nerd Font wants
to do.

One solution would be to have font-patcher properly set up / divided in
many .py files, and to create one monolithic font-patcher from all the
sources on demand (via github actions or manually when someone pushes
changes to any of the constituends). That approach is taken by a lot of
C++ 'header only libraries' that originally consist of a lot files but
create one big 'all in one' file automatically from all the small files.

For now I guess we can live with the duplication, but we need to think
about a solution, as this will bite us sooner or later.

Signed-off-by: Fini Jastrow <[email protected]>