[rush-lib] Ensure async telemetry hooks flush during error report

[MichaelSitter]

Summary

Hey team, I raised a question in Zulip about an issue with custom plugins using the the flushTelemetry hook:

https://rushstack.zulipchat.com/#narrow/stream/262513-general/topic/flushTelemetry.20hook.20receives.20no.20data.20for.20failed.20operations/near/432975837

Summarizing here, RushCommandLineParser doesn't wait for the flushTelemetry async tasks to finish for processes which ended in failure.

Details

I created a reproduction for this issue here, with a really simple plugin that just taps the telemetry and re-writes it to a custom file. You should be able to see the following:

• rush build --to rush-flush-telemetry-example-plugin: Task succeeds, and the custom telemetry file gets written with the telemetry report.
• rush build --to my-app: Task fails, and the custom file gets written but contains no data.

We did a little more digging & it looks like the tap hook actually works, its just the async hooks that aren't getting processed correctly. The approach I used is moving the process exit into the finally of ensureFlushedAsync. I think this is probably the right behavior, but this is a change in behavior for failed operations since it'll delay the process terminating until the telemetry hooks can be safely flushed. If this isn't an acceptable change in behavior, could we consider supporting this behind a feature flag? Or if there is a better approach I'm missing very open to suggestions. 🙇

How it was tested

There is a new test file I added, RushCommandLineParserFailureCases which is separate from the existing test file to avoid the mocking imports. This necessitated moving some of the test setup code into another file so it could be reused.

Impacted documentation

None, this addresses an issue with the native telemetry.

[MichaelSitter]

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