Step 2 - Extract sidebar_nav component from collapsible_panel

• Step 1 - Clean up some collapsible_panel things
• Step 2 - Extract sidebar_nav component from collapsible_panel
• Step 3 - Decouple resizeable_panel from collapsible_sidebar

What does this MR do?

In preparation for decoupling resizable_panel from collapsible_sidebar, this MR:

• Moves the rendering of the sidebar tab buttons into it's own component.
• Removes the getter isActiveView... Getters which return functions can be confusing, and this one doesn't necessarily do a whole lot.

Screenshots

References

Related to #204821 (closed)