Add darwin-universal target

[paulober]

Since many binaries are currently build for macOS universal I guess also many darwin-x64 and darwin-arm64 vsix packages are the same.
Therefore I would suggest adding a new target darwin-universal which would if uploaded replace the downloads for darwin-x64 and darwin-arm64 without using double the storage on the Microsoft servers. But it would still allow to later publish a darwin-x64 for example which would then label the darwin-universal as darwin-arm64 and upload the new package as darwin-x64.

[paulober]

Currently the publish command does support adding darwin-x64 and darwin-arm64 but package not. So if you have a platform dependent package are you supposed to package all platforms platform dependent but for macOS package universal and publish platform dependent?

[sandy081]

CC @isidorn

This requires support in Marketplace.