[Enhancement] Export existing visualizations to vega

[joshuarrrr]

Posting on behalf of a user who doesn't have a GitHub account

Is your feature request related to a problem? Please describe.

We have a dashboard that we manually filter by using the Controls visualization. When adding a filter, the whole dashboard is affected, but we would like some of the visuals to stay the same and not inherit/implement dashboard filters.

Describe the solution you'd like

The only current way to build visualizations that ignore filters is to use the vega visualization (where global query, filters, and time range can be selectively included as part of the spec. But because we already have many existing visualizations, we'd prefer not to re-create them from scratch. It would be easier to just export them to vega, tweak the dashboard filter part and import them back.

Describe alternatives you've considered

Alternatively, or additionally, it should be possible to configure dashboard visualizations to ignore global filter updates; a filter equivalent to what's proposed for date ranges in #1242

[joshuarrrr]

Making visualization types more portable between different editing tools and environments is something well within scope of the visualization framework unification project: #2840

After completing #2819, we will already have the technical capability to render previously created visualizations in vega-lite, so then we'd just need a UI flow for users to what's described here.