Notebook Outline View enhancements

[Yoyokrazy]

Tracking issue for a number of improvements to the notebook TOC/outline view

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Run in Section

Related issues: #187601 / #199992 / #180272

Feature Items:

• Toolbar in outline view entries (Support toolbar in notebook outline pane entries #207498)
• Context menu on notebook stickyscroll elements (Run in Section for notebook sticky scroll context menu #205307)
• Run button in folded cell hints (Folded cells run-in-section #205315)

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Visual Polish

Related Issues: #200060 / #199969 / #147007 / #174104 / #134055

Feature Items:

• Header related options
  • Setting controlling what md content shows in outline view "notebook.outline.showNonHeaderMarkdownCells": boolean (Add setting to exclude non-header md cells from notebook outline view #207771)
  • Strip non-header content from header cell entries (looks fixed during a PR~7 months ago. header cells currently only show headers. Will close stale issues as I find them)
• Code cell related work
  • Show symbols as children of code cells (Add code cell symbols to nb outline + debt fixes #208323)
  • Figure out how to show more relevant content for code cell outline entries. (tabling this for now... no good solution with our current tools)

Up for Discussion:

• Remove the markdown symbol, just visual noise
• Align md icons with go to symbol view
• What should the content be for code cell entries? First line? First symbol?

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Debt/Engineering

Related issues: #200873

Feature Items:

• Refactor work to share outlineModel between sticky scroll, outlineview, & folding model
  • lot of unnecessary recomputes, all happen 3x per event firing. Could be a shared model between them.

[Yoyokrazy]

Related work for cell execution in folded cell hints is shipped with: #205315

[Yoyokrazy]

Adding in related work on icon alignment between views: #206829