Test lazy WorkspaceSymbolProvider

[jrieken]

• any @joaomoreno

tests #890

Test that you can now implement a 'lazy' workspace symbol provider. That is one that returns incomplete symbol information but offering a resolve method that is invoked when a symbol is selected in the UI.

[jrieken]

FYI - to test against the latest API do the following:

• open your extensions package.json file
• change the engine.vscode property to *
• run npm run postinstall (assuming you have the vscode module as dev-dependency)
• undo the engine-version change from step 2

[joaomoreno]

Thanks for the tip on the engine change!