Need to add unit or integration tests (not e2e for now) for Bicep deployment

need for e2e tests tracked here: https://github.com/Azure/bicep/issues/6827

The more pressing need is for the ability to test the extension UI in an easier way to prevent regressions like https://github.com/Azure/bicep/issues/11683. The tricky part is unit testing with the UI inputbox interaction. Two options:

1) functionality can be refactored to more easily support unit tests
2) we can use the IAzureUserInput test capability natively supported by the shared package @microsoft/vscode-azext-utils. Last time I looked into this, there were complications due to webpack and due to the fact that we're somewhat behind on updates (see https://github.com/Azure/bicep/issues/11155 assigned to me). The advantage of getting this done is easier testing for all UI scenarios. I'm willing to help figure this out but can't take on the task right now.

Note: The inclusion of the experimental deployment pane adds another layer of testing needs here, don't know if that has already been solved or not, but I expect it should be naturally easier to unit test.