This patch adds a left aligned sidebar to the spreadsheet editor. This Sidebar can be used to navigate the geometry component types and attribute domains. It also provides a quick overview of domain sizes. It replaces the two dropdowns in the regions header. Next step will be to add the domain cycling shortcut using the CTRL + mouse wheel. Reviewer: Dalai Felinto (dfelinto), Julian Eisel (Severin), Hans Goudey (HooglyBoogly). Differential Revision: https://developer.blender.org/D11046