Improve `Viewport.follow_viewport_enabled` description to be less confusing

**Your Godot version:** 4.3

**Issue description:**
The description for `follow_viewport_enabled` is currently as follows:
> If enabled, the CanvasLayer will use the viewport's transform, so it will move when camera moves instead of being anchored in a fixed position on the screen.

This seems rather confusing, as both options described sound equivalent. "Moving when the camera moves" sounds like it will remain visually in the same place on the screen, but the alternative is "being anchored in a fixed position on the screen".

I will put together a little project to test this and determine what it actually does in practice, but my current guess is that "anchored in a fixed position *on the screen*" should be replaced by something like "anchored in a fixed position *in the world*"?

**URL to the documentation page (if already existing):**
https://docs.godotengine.org/en/stable/classes/class_canvaslayer.html#class-canvaslayer-property-follow-viewport-enabled