Add API to programmatically minimize a pane

[ddaribo]

Is your feature request related to a problem? Please describe.

Programmatically maximizing a pane is possible by assigning the following properties:

targetPane.isMaximized = true;
this.dockManager.maximizedPane = targetPane;

For minimizing, the below should also work:

   if (this.dockManager.maximizedPane) {
            this.dockManager.maximizedPane.isMaximized = false;
            this.dockManager.maximizedPane = null;
   }

However, for apps having the compilerOptions strictNullChecks set as true in tsconfig.json, the compiler lights up with the following:

Describe the solution you'd like

Make the maximizedPane nullable, or expose methods to maximize/minimize panes programmatically.

Describe alternatives you've considered

The above snippet and setting the strictNullChecks to false.

Additional context

Sample here. The compiler does not error on the dev environment.