Add action for toggling editor group maximize

[akbyrd]

We have actions to maximize an editor group and to reset editor groups sizes: workbench.action.minimizeOtherEditors and workbench.action.evenEditorWidths but there's no way to bind these is such a way that the same keybinding can toggle between maximized and not maximized.

I'd like to request an action such as workbench.action.toggleEditorGroupMaximize.

This is related to #24163 but I think is a better solution.

[bpasero]

I pushed a new action "Toggle Editor Group Sizes" with command ID workbench.action.toggleEditorWidths that will:

• maximize the active editor group unless maximized already
• even out the editor widths otherwise