Consider options for how/when new editor action bar UI affordances appear

[juliasilge]

In #7237 we added a new checkbox control and toggle control for the editor action bar, for extensions to use. In quarto-dev/quarto#698 we then added these controls for use in the Quarto extension. Super exciting to see these in use! 🎉

If I open a project where a Quarto file was previously opened, the "Preview" button with its label shows up immediately, but the other two new controls take quite a while to show up:

action-bar.mov

This screen recording was done with a dev build and the delay is ~5 sec. Certainly it will be much less in a release build, but we can expect it to be similar to the experience we currently get with the Posit Publisher extension (>1 sec easily). From my perspective, it feels a bit more disorienting than that example, though, because whole new UI affordances show up quite "late", rather than a single icon.

The current alternative we could use to is to have the UI affordances themselves show up at the same time as the "Preview" button, but then, for example, the checkbox would check itself a second or two later.

• Which is better UX for now, to have the whole UI show up "late" or to have them adjust themselves "late"?
• Do we have any options to have less delay overall for this kind of treatment? (We don't currently know of any.)

[juliasilge]

For a quick path to experience the delay:

• Have a workspace open with a .qmd file open
• Close the workspace (for example, from the top right project switcher)
• Wait for Positron to be in the "no workspace" state
• Open the original workspace (for example, from the top right project switcher)