shortcut to collapse all in outline view

[glacjay]

[vscodebot]

(Experimental duplicate detection)
Thanks for submitting this issue. Please also check if it is already covered by an existing one, like:

• Outline view: no symbols shown after collapse and expand (#69667)
• Add Visual studio collapse feature (outlining) (#60054)
• outline (#66736)
• Outline view settings (#62572)
• Outline view: collapsed by default (introduce optional setting?) (#53262)

[sandy081]

@jrieken Outline view is not a custom view and is contributing collapse all action by itself.