- Closes#8386
- Attempts to execute `<expr>.default_visualization` to query the engine for the *correct* fallback type
- If that is not possible, falls back to checking `inputType` - first for an exact match, then falling back to `Any` (i.e. the text/JSON visualization)
- Does not decide fallback based on the shape of the returned JSON
# Important Notes
Contains pretty significant refactors of `VisualizationMetadata` to allow it to be unset.
- Closes#8179
# Important Notes
- ⚠️ These tests are currently *not run* on any CI workflow.
- There is some unused code for mocking the PM. This has been intentionally kept, as this may be useful in the future.
Note that this may be useful for testing the dashboard, however the dashboard is currently only tested in cloud mode
- that is, without the backend switcher, and with only the remote backend available. As such, currently it uses HTTP API mocks, and no PM mock.