Add filter for original fonts vs Muscovite fonts

In Cyrillic fonts there are two main types of fonts. The first type of those are sometimes called Bulgarian type or handwritten cursive or classic. The second type is Russian type or press (machine) type or Muscovite. The names are not that much important in my opinion. You can differentiate those two types by looking at д or the л letters. The first type has triangular д and triangular л. And the second type has flat д and flat л. Also some of the other letters are different; like г and к.

When searching at https://fonts.google.com/ there is no filter for those two types of fonts. It would be nice to have filter for those two types.

Some examples of "original" Cyrillic font types:

* [Pasifico](https://fonts.google.com/specimen/Pacifico?lang=bg_Cyrl&script=Cyrl)
* [Poiret One](https://fonts.google.com/specimen/Poiret+One?lang=bg_Cyrl&script=Cyrl)
* [Sofia Sans Condensed](https://fonts.google.com/specimen/Sofia+Sans+Condensed?lang=bg_Cyrl&script=Cyrl)
* [Ledger](https://fonts.google.com/specimen/Ledger?lang=bg_Cyrl&script=Cyrl)
* PT Serif BG Beta Regular

Some examples of "Muscovite" Cyrillic font types:
* [EB Garamond](https://fonts.google.com/specimen/EB+Garamond?sort=alpha&lang=bg_Cyrl&script=Cyrl)
* [Liter](https://fonts.google.com/specimen/Liter?sort=alpha&lang=bg_Cyrl&script=Cyrl)
* [Roboto Mono](https://fonts.google.com/specimen/Roboto+Mono?sort=alpha&lang=bg_Cyrl&script=Cyrl)

More info: https://cyrillic.bgweb.bg/

No repository files, tests, or entry points are named. Start by reviewing the proposed Bulgarian and Muscovite font examples and the linked reference, then determine how the requested distinction fits the existing Google Fonts search; done means an agreed, implementable classification and filter behavior.

Written by the indexing model from the issue text.