Resolve #3482394: "Move components from topbar to sidebar"

Closes #3482394

This MR:

• Moves the components and section menu to the primary panel under the Library tab
• The Library tab is now managed by redux in primaryPanelSlice.ts so the 'Add section' and 'Add component' functionality still works.
• Components accordion dropdown is open as the initial state (choice I made)
• Renamed PrimaryMenu.tsx -> PrimaryPanel.tsx to be consistent with ContextualPanel.
• Renamed addMenuSlice.ts -> primaryPanelSlice.ts
• Commented out old AddMenu code (files in /topbar/add/) with a todo comment at the top to reuse when the modules menu work happens.
• Renamed the enum NodeType -> LayoutItemType ('component' | 'section') in primaryPanelSlice.ts to avoid confusion with the LayoutNode enum ('slot' | 'component' | 'root') in layoutModelSlice.ts
• Added scrolling to PrimaryPanel