Adding dotnet language server for API Reference support

[gracegoo-stripe]

Addresses #175

In order to support API hover reference for dotnet projects, we needed semantic understanding of the code the user is writing. The dotnet language server identifies when a user is hovering over a Stripe method and returns hover content back to the extension with the link to the relevant point in the doc.

This PR is a combination of previous PRs + a rebase with master:

• Set up dotnet server and connect it to the extension: Move dotnet server into vscode repo and connect language client #236
• Implement API reference handler with semantic model analysis: Move dotnet server into vscode repo and connect language client #236
• Implement Solution syncing: Syncing Solution and improving some dev workflows #271
• Add conditional server startup logic based on workspace project: Adding conditional language server startup and passing in project from user workspace #275
• Using dotnet install tool extension to acquire the dotnet runtime: Using the .NET runtime extension to acquire our executable  #281
• Get the project file from the client: Adding conditional language server startup and passing in project from user workspace #275
• Update the configuration file with real entries: Update API reference config #274
• Update debugging steps since we've merged the repos
• Publishing: Add publishing step for dotnet language server #276

Testing

On windows: https://user-images.githubusercontent.com/75757829/122482958-657a1900-cf86-11eb-82a0-315c898f803e.mp4
(My screen capture software on windows only lets you record the active window so we can't actually see the link open)

[vcheung-stripe]

Sanity checked the individual PRs, lgtm