Ensure workspace is fully initialized before discovering tests

[vinistock]

Motivation

@alexcrocha noticed that when opening the test explorer while the LSP is booting, the test items inside a file wouldn't be populated.

There are two reasons for it:

1. We need indexing to be completed first before we can discover tests, since discovery requires ancestor linearization and there are no guarantees that we already found all the pieces in the middle of indexing
2. There was a bug in fetching or lazily activating a workspace that may result in double workspace activation

Implementation

There are a few parts to the solution:

1. I started capturing the promise for when indexing ends in the client, so that we have a convenient way of checking if it's over. We were already doing it in tests and now we need it for the controller
2. Our handling with the workspacesBeingLaunched was spread around multiple places, which is a recipe for disaster. I moved all related handling inside the function that activates a workspace, so that no matter from where we're activating, it is guaranteed to be taken into consideration
3. I also turned workspacesBeingLaunched into a map of workspace index to activation promise. If a workspace is in the middle of being activated, this gives us the opportunity to return that promise so that other parts in the code can await the same activation process
4. Finally, I started only setting the workspace after we finished awaiting its start. Setting the workspace in the map before invoking start means that invoking getOrActivatedWorskpace will find the non-started workspace and lspClient will be undefined

Automated Tests

Adjusted existing tests.

[vinistock]

• Ensure workspace is fully initialized before discovering tests #3203 👈 (View in Graphite)
• main

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