Fix compile errors and warnings

[aeisenberg]

Here are a few behaviour preserving changes that I made that helps avoid some compiler errors and warnings.

• Updated launch config for mocha (tests are failing, but at least it launches)
• Updated versions in package-lock.json
• Updated @types/vscode to latest
• Removed two onCommand triggers that are now deprecated
• Added const vscode: VsCodeApi to global.d.ts to get properly typed references to vscode instance in the webview.
• Converted return to return undefined where appropriate to make compiler happy.
• Also, a handful of other errors that the compiler was complaining about.

[aeisenberg]

@EasyRhinoMSFT, would you be able to take a look at this?

[aeisenberg]

Thanks for the review!