Make ortho projection more discoverable and easier to use

[pjcozzi]

@bagnell can you please do this next to polish #5021?

• Add an "Orthographic Projection" Sandcastle example that creates the Projection Picker widget and perhaps loads a glTF model or creates a box geometry.
• Is it possible to move the _switchToPerspective and _switchToOrthographic functions from the widget to a more generic place so that apps using their own widgets can easily switch between projections? This is similar to decoupling the morph from the scene pick widget and decoupling the geocoder from the geocoder widget.

Part of #4678