Notebooks: As a builder, I want to easily switch to Flux script while building a query

We found in our user research that users who are familiar with Flux quickly switch to the script editor, often doing so in Data Explorer. Currently, we're hiding Convert to Flux within the panel dropdown menu, which could be a large deterrent for Flux script users looking for an easy way to switch to Flux.

To make this experience similar to what we currently have in Data Explorer, let's place Convert to Flux/Script Editor directly on the Query Builder panel.

Data Explorer Experience:

New Design:

Questions:
- How often do users switch to Script Editor in Data Explorer? Do we have the stats to support this design change?
- Do we want to call this feature "Script Editor" or "Convert to |> Flux"?
- Similarly to what's included in Data Explorer, would we want to allow the user to go back to the Query Builder, but just include the message that they'll lose their work?