Clean up Mocha test contamination between Resources view and FlinkLanguageClientManager

We started seeing a lot of logs relating to these two areas:

This may be caused by some event emitter being fired in tests and the (real) provider/manager not being stubbed, so their listeners handle the callbacks for a given event (or multiple) which leads to a lot of test log noise.

If left unchecked, this could cause test flakiness and/or timeouts.

Inspect the Mocha tests covering the Resources view and FlinkLanguageClientManager, then trace which event emitters invoke real providers or managers instead of stubs. Run the affected test suite and confirm that listener callbacks no longer produce cross-test log noise, flakiness, or timeouts.

Written by the indexing model from the issue text.