Preparations for a 1.0.0 release

In the past while, we've gotten a lot of really great features into the extension. Many from the language server, and a lot of integration into the extension itself. More up to date vscode-languageclient, more uniform support across marketplaces (soon), RelaxNG, new formatter, out-of-the-box support with the binary server on supported platforms, eventual migration to GH actions. I think we should start to consider what needs to happen for a 1.0.0 (mature) release.

This might involve a lot of different things :

• evaluating what we should keep as internal/provisional vs. becoming API
• How we address/respond to critical issues
• looking at improvements to our release process
• whether these changes may hurt/benefit other consumers of our work

Would be good to hear people's thoughts on this. Are there any sets of features severely lacking ? Is there any reason to continue to stay in the preview mode ? See https://devblogs.microsoft.com/visualstudio/new-preview-label-for-visual-studio-extensions-2/ .

We could use the time after 0.24.0 to work towards this.