Error popup and Bicep output missing information to diagnose exceptions

While investigating #11467, we were only able to diagnose the problem by doing a screen sharing session, and happening to notice the unusual URI format in the logs.

There was no exception information presented to the user either in the error popup in VSCode, or in the Bicep output logs with full verbosity enabled.

To make similar issues simpler to diagnose in future, it's worth using the repro we have for the issue to try and understand why we weren't surfacing more information about the problem that could have helped us figure it out without a screen share session.

Start with the repro referenced in #11467 and investigate why exception details are absent from both the VSCode error popup and Bicep output logs at full verbosity. Compare the information available during the screen-sharing diagnosis with what users currently see; done means both surfaces expose enough exception and URI information to diagnose similar failures without screen sharing.

Written by the indexing model from the issue text.