Document how to resize a SubViewportContainer to avoid stretching
Document how to resize a SubViewportContainer to avoid stretching

This closes #27534.

(cherry picked from commit f818a99d0b290319665f0cfb4f7024b451fd78aa)

ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot