Test Outline View

[jrieken]

re #5605

• anyOS @rebornix
• anyOS @sbatten

Complexity: 3

We have added a preview of an outline view. Test that

• it is disabled by default and can be enabled as extra view in the explorer
• it shows the outline for the active (workbench) editor
• it shows an outline tree when there is an outline provider registered and shows a good message when not
• symbols can be sorted in different ways
• the editor selection can be tracked in the outline tree
• there is a filter box that allows to narrow down on outline items
• there is (unbound) command outline.focus that puts focus into the outline