Test: Horizontal scrolling in trees/lists

[joaomoreno]

Tests #63684

• macOS @sandy081
• linux @chrmarti
• windows @roblourens

Complexity: 3

We used to have a workbench.tree.horizontalScrolling setting which enabled horizontal scrolling across all (old) trees in the workbench. This setting now works for all lists and new trees as well. As you enable it, make sure the following trees all work correctly and properly scroll horizontally:

• References widget
• Debug
  • Loaded scripts view
  • Call stack view
  • Debug hover
  • Variables view
  • Watch expressions
  • Breakpoints
• Explorer
• Open Editors
• Problems
• Search
• SCM View

The following lists/trees should not have horizontal scrolling:

• Debug Console
• Notifications
• Quick Input
• Keybindings Editor
• Extensions view
• Runtime Extensions