[builder] move the mac names specific to VF to platform 3?

I transmit here the conversion we had in the group chat to keep an archive and have more opinions:

Original question:
Is there a reason why we have nameID 25 + custom names linked to STAT and FVAR (25* to 27*) in platform 1 instead of platform 3 with the rest of the name tables?

Adam said:
> As we know, variable "OpenType" fonts have been working in Mac OS since Mac OS 7.5 released in 1994, and if packaged as TTF, since the first version of Mac OS X published in 2001. This is because TrueType-flavored variable fonts are backwards-compatible with TrueType GX Variations. But until Mac OS X 10.13 High Sierra (2017) or 10.14 Mojave (2018), not sure now, the predefined instances in the fvar table only worked if their names were registered in the Mac classic PID 1 EID 0 name table branch.

> Even though macOS started preferring the 3.1 name entries for other names, Apple’s TT GX code was dormant for years so nobody updated that part, until, I think Mojave. There is still some portion of users of Mac OS X Sierra and High Sierra, especially since older Apple hardware is actually surprisingly resilient, and still yields good prices on secondary markets. In some countries, a seriously older Mac with old Mac OS X is still a machine that is much in demand.

So main concern is backward compatibility.

Although, Dave recalled that these OS don't support VF so well.

Also Olli (@moontypespace) told me by email:
> Even Apple’s SFCompact.ttf system variable font does not contain Mac name table entries anymore.

cc @vv-monsalve @davelab6 @twardoch @m4rc1e