Auto-install brighterscript versions

[TwitchBronBron]

Update the brighterscript version picker to show the following options:

• use vscode's version
• use workspace version
• use latest prerelease
• specific in-progress version
  • lsp-rewrite
  • v1
    -stuff
• Pick from release list
  • 1.0.0
  • 1.0.1

Implementation:

• when a specific version is selected, vscode should install that version from npm (or github depending on where the release is coming from) into a temporary or extension-specific storage (i.e. NOT in the workspace folder), and then use the lsp from that folder

This provides the benefit of having users jump onto different release tracks without needing to mess with npm. This also allows many devs to not need npm at all if they're not using bsc for building.