refactor+fix trace server url initialization

[paul-marechal]

Both TraceServerUrlProviderImpl and TraceViewerEnvironment are
riddled with concurrency issues. A lot of events happen asynchronously
but the logic doesn't take this into account, leaving the application
vulnerable to race conditions when trying to fetch the trace server url.

Refactor by removing TraceViewerEnvironment and moving its
functionality directly into TraceServerUrlProviderImpl, add logic to
prevent race conditions.

Unfortunately I was forced to introduce a LazyTspClient which is
implemented as a proxy to a TspClient and defers all async method
calls until baseUrl is asynchronously resolved. This only works because
all TspClient methods are asynchronous.

The proxy is a temporary measure which should buy you time until
you guys rework the frontend initialization sequence to make sure
everyone expects and handles the asynchronous steps.

Fixes #493
Closes #499

[paul-marechal]

Some notes about the use of the LazyTspClient: classes seem to want to synchronously get a reference to a TspClient, but all work done through it is asynchronous. All places that uses the TspClient deal with asynchronous calls. This makes me think that it should be possible to instead pass around a promise to a TspClient and first await on this before using its async methods. We're dealing with async stuff anyway when it gets time to use it.

[bhufmann]

It looks good to me and it works locally and in GitPod. Thanks for improvement! @paul-marechal, could you please answer my question.

[paul-marechal]

PR is good for re-review/merging again!

[bhufmann]

I tested it locally (with default URL) and in GitPod where a custom URL via the TRACE_SERVER_URL environment variable is used. Both work well. Thanks for the contribution.

[paul-marechal]

Ok I am ashamed of continuously removing your approvals but this wasn't just nitpicking.

The value returned by getTraceServerUrlPromise() used to be set once, and any subsequent call would only ever return the initial value. This is now fixed.

Thanks for bearing with me!

[bhufmann]

now I found something :-) Could you please update it?

[bhufmann]

The normalizeUrl() method change in one of the previous commits causes that it won't work in GitPod anymore. See comment and suggestion below.

[ebugden]

Thank you all for working on this! 🌳

[bhufmann]

Looks good to me. Thanks for the contribution.