Weight Axis for VF: please add one intermediate named instance every 100 units systematically

The majority of VFs here, with weight axis, have a named instance every 100 units (depending on the extent of their weight axis). But, for VFs created before April or May 2021, every now and then a Medium or SemiBold weight, sometimes both, has been forgotten, although the API offers them.

I find myself with users who choose a font from https://fonts.google.com/, where all intermediate weights are displayed, and complain that I give them a "crippled" version when I give them the VF for software that only supports named instances (and giving them the static version is not a solution either, until fonttools/fontbakery#2616 is fixed).

Also, I'm not making a difference in this request between the `fvar` and `STAT` instances, but they don't always sync, so the problem overlaps sometimes with fonttools/fontbakery#3267.

Of course my request is not intended to ask that all the fonts switch to a weight axis that goes from Thin to ExtraBlack, but simply, if a VF has a weight axis that goes from 400 to 700 (for example), there should be Regular, Medium, SemiBold, and Bold instances.

* Alegreya lacks SemiBold
* Antonio lacks ExtraLight, Medium
* Assistant lacks Medium
* Caveat lacks Medium, SemiBold
* Cinzel lacks Medium, SemiBold
* Cuprum lacks Medium, SemiBold
* Domine lacks Medium, SemiBold
* Fraunces lacks ExtraLight, Medium, ExtraBold
* Ibarra Real Nova lacks Medium
* JetBrains Mono lacks SemiBold
* Kufam lacks ExtraBold
* Merriweather Sans lacks Medium, SemiBold
* Open Sans lacks Medium
* Red Rose lacks Medium, SemiBold
* Sora lacks Medium
* Space Grotesk lacks SemiBold
* Varta lacks Medium