Initial integration with Positron's inline cell execution API

[jmcphers]

This change prepares the Quarto extension to work with Positron's upcoming inline output features.

There changes are pretty minimal for now. When inline output is enabled (via a setting):

• The code lens is disabled (as it duplicates Positron's built-in toolbar)
• Code is executed using the inline execution API instead of the console execution API
• The title of the Insert Code Cell command in the toolbar is not shown, to conserve toolbar space and make room for the kernel picker (we do this all the time since it's hard to do conditionally)

Part of posit-dev/positron#5640.

[juliasilge]

Looks good to start out with! 🙌

I checked that regular console execution is all still working well with these changes.