Publish platform-specific binaries & pre-releases to open-vsx.org

[datho7561]

According to eclipse/openvsx#406, it seems open-vsx.org supports platform-specific extensions. It would be neat if we published platform specific extensions for open-vsx.org as well.

[rgrunber]

Before we adopt this, we should follow :

https://open-vsx.org/extension/jbangdev/jbang-vscode
https://github.com/jbangdev/jbang-vscode/blob/main/.github/workflows/ci.yaml#L72

and maybe try it out on a flavour of VS Code that uses OpenVSX as the default marketplace.
According to @fbricon , there is no distinction between a release and a pre-release as far as the marketplace goes. We should confirm platform specific vsix work the same way as we expect.

[rgrunber]

At least for pre-releases, there is no distinction currently between itself and a release in the UI. The UI allows installing pre-release as if they were regular releases. redhat-developer/vscode-java#2587 (comment)