Format names last, first

[tdegeus]

Is your feature request related to a problem? Please describe.
I would like to format names in the output as last, first

Describe the solution you'd like

bibtex_str = """
@ARTICLE{Cesar2013,
  author = {Jean César and T. W. J. de Geus},
  title = {An amazing title},
  year = {2013},
  volume = {12},
  pages = {12--23},
  journal = {Nice Journal}
}
"""

import bibtexparser
import bibtexparser.middlewares as m

layers = [
    m.SeparateCoAuthors(True),
    m.SplitNameParts(True)
]
library = bibtexparser.parse_string(bibtex_str, append_middleware=layers)

layers = [
    m.MergeNameParts(True),
    m.FormatNames("{last}, {first}"), # to be discussed!
    m.MergeCoAuthors(True)
]
print(bibtexparser.write_string(library, prepend_middleware=layers))

should then print

@ARTICLE{Cesar2013,
  author = {César, J. and de Geus, T. W. J.},
  title = {An amazing title},
  year = {2013},
  volume = {12},
  pages = {12--23},
  journal = {Nice Journal}
}

Use cases
In my experience, certain styles need this.

Describe alternatives you've considered

Remaining Questions (Optional)
Please tick all that apply:

• I would be willing to to contribute a PR to fix this issue.
• This issue is a blocker, I'd be greatful for an early fix.

[tdegeus]

Seems addressed here #422 and discussed in #421

[MiWeiss]

Seems addressed here #422 and discussed in #421

As these are merged and closed now, I am also closing this issue. If anything remains unsolved for your usecase, we may be able to address it as part of #439 (which is conceptionally related), or in a new issue, as you prefer.