Add a large world coordinates demo

[Calinou]

This allows testing double-precision builds and see if they work as expected, while providing an interactive demonstration.

Some core shaders fail to load when using a double-precision build (which leads to ambient shading being pure black); I don't know why. This doesn't occur on a brand new project.

Screenshots

Using single-precision build (including official builds)

Using double-precision build

[joao-pedro-braz]

About some core shaders failing to load, for me that only happens when using the Mobile render.
Forward+ works flawlessly.

[zf-moth]

I tested both Godot versions and looked over the code and this looks great to me.