Preserve selected instrument when switching resources

[JamesNK]

Change metrics page to preserve the selected instrument when switching resources if the new resource also has that instrument.

For example, http.client.request.duration is selected in App1. Switching to App2 keeps http.client.request.duration selected if App2 also has values. If App2 doesn't have http.client.request.duration then the instrument is cleared (current behavior).

The goal is to make switching between resources more seamless.

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Also, I wrote a bunit test for the metrics page that tests this change.

Microsoft Reviewers: Open in CodeFlow

[JamesNK]

@vnbaaij I'm confused why this is needed. I found that it is required for the other change event to trigger in a unit test.

This is what is in the unit test:

        var resourceSelect = cut.FindComponent<ResourceSelect>();
        var innerSelect = resourceSelect.Find("fluent-select");
        innerSelect.Change("TestApp2");

If ValueChanged isn't bound on FluentSelect then SelectedOptionChanged is never called. Adding ValueChanged makes it work 🤷