Support toolbar in notebook outline pane entries

[Yoyokrazy]

re #206308

Contributes a toolbar to the outline entry items in the notebook outline pane. Toolbar continues some or none of the following actions:

• Run Cells in Section
• Run Cell
• Fold Section

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Future thoughts:

• Fold Section wording
  • This technically performs a "toggle folding range" action, but I'm hesitant to use the word toggle as it only controls the notebook editor view state, not the outline view state. Maybe an item for the future.
  • Could be more fitting to have two separate actions, one for Fold Section and one for Expand Section. Would be easy to have the actions only show depending on the cell's folding state via a context key.
• Add a minimum time to the spinner in the outline view, similar to the cell execution status item in the cell status bar (think this was 500ms?)

[rebornix]

Let's go