Scene Interaction: Add fallback when there's nothing to raycast against.

[FrayedFunction]

Description

Objects can't be placed into empty scenes because SceneInteraction breaks when there's nothing to raycast against.

Steps to Reproduce

1. Open an empty scene
2. Attempt to place an object

Expected Behaviour

Objects should be able to be placed freely in an empty scene

Actual Behaviour

Placer freezes at world origin, or on the last collider hovered over.

Possible Solutions

Could fallback to:

• Mouse position
• 2d mode (currently being worked on in feature/2dSupport)
• Plane Projection

[FrayedFunction]

I think plane projection makes the most sense here as Its y can be set to 0 which feels natural placing objects on the worlds floor. Will expose the default height property in the settings menu.