- make them both use .theme-twisty to show an arrow icon.
- move some specifics stylings of SourcesTree to the base class.
- make SourcesTree use the arrow React component provided by Tree class.
- use .theme-twisty instead of .arrow (which already implements rotation and colors on expand). But it uses "open" instead of "expanded" classname.
(VirtualizedTree was already using theme-twisty)
This impacts the Source Tree, ObjectInspector (console, debugger), Watch Expressions, memory panel (dominator view).
Differential Revision: https://phabricator.services.mozilla.com/D215637
e0c53a42c4