The patch name is probably off (the actually added function is GetPackagesByPackageFamily and not GetCurrentPackageFamilyName)?
FWIW The function is implemented in Proton for a while: https://github.com/ValveSoftware/wine/commit/4f20827500da2d90b6b18163f18d6ff...
The reason it hasn't been sent upstream yet is that for original occasion (Forza Horizon 4) the stub won't work, it needs the actual data returned. and the implementation apparently won't do that without the information present in registry. Proton has another patch for that right before this one: "wine.inf: Create package repository for VCLibs.140.". But that is essentially a workaround, doing it properly is a bit more complicated and involves introducing the package repository in Wine to be updated from builtin VC components.
So the question is, does the app concerned here depends on GetPackagesByPackageFamily returning success? If not, maybe worth considdering taking the implementation as by itself it is probably correct and has a test. Not entirely sure though, maybe it doesn't worth the complication until the actual package info is there.