extension: Separate UI into Analyze and Visualize tabs.

[parkerziegler]

A core part of reviz's premise is that users can not only analyze existing visualizations but also generate new visualizations by filling program holes with column names. Given this vision, we want to separate the extension UI into separate Analyze and Visualize tabs. The current content of the extension will fall into the Analyze tab. The Visualize tab will host, at a minimum, a Code Mirror editor for the partial program and an output space to render the new visualization.

For this issue, the scope is to:

• Use @radix-ui/react-tabs to split the UI into separate Analyze and Visualize tabs.
• Add the scaffolding for the Code Mirror editor filled with the partial program.