Limit the editor zoom and freelook speed based on camera settings

[aaronfranke]

Just for fun, I recently decided to zoom out as far as Godot would allow me to. After zooming out such that the indicator says about 4 quadrillion, Godot started using gigabytes of RAM and my Linux computer froze due to running out of memory. So, I set out to add some limits to the zooming to prevent this, but I realized we could do much better than just limiting to a quadrillion or so, we could actually set some sensible and dynamic limits.

This PR sets a limit for zoom and freelook speed based on the camera's near and far clipping planes, while also having some hard-coded limits (10 thousand for single precision, which allows fitting the usable area in the whole screen with some margin, and 1 trillion for double precision, which is slightly smaller than double's usable area).

With this PR, the focused point is guaranteed(*) to be inside of the camera's clipping area, while previously it was super easy to zoom in a way that made the object invisible.

Also, since there is now both a minimum and maximum, the bars now have an accurate top and bottom end. Previously, zooming out would just exponentially get closer to the bottom of the bar.

I requested a review from @Calinou and @Zylann since they have touched this code before.

(* technically it can get out of the clipping area if the near and far planes are extremely close together but that's not normal usage of the editor camera and at that point you'll have a hard time fitting anything into the clipping area anyway)

This fixes #37034, fixes #40014, fixes #43467.

3.2 version: https://github.com/aaronfranke/godot/tree/3.2-limit-zoom

[Calinou]

Tested locally, it works as intended.

[akien-mga]

Thanks!

[akien-mga]

Cherry-picked for 3.2.4.