Each member is a key (resolved registry-first - a registered entry, else a plain command), a
divider ('-' / null, leading / trailing / adjacent ones collapse), or an inline entry.
An entry with its own render drives the control; else members ⇒ a nested CommandGroup, otherwise
a CommandButton.
Walks a member list (CommandButtonEntry.members) into React nodes - the shared surface primitive. Both the popup surface (CommandGroup) and the toolbar surface (
CommandToolbar) render through this; they differ only in RenderMembersOptions.