Editor: Custom theme previews are cropped when they dont fit in the designated area without ability to pan around and see all contents #124481

Tested versions

4.7.2
4.8.dev7

System information

Windows 10 - Godot Engine v4.8.dev.custom_build.5ec712e22 (2026-10-14 02:51:44 UTC) - https://godotengine.org Vulkan 1.4.315 - Forward+ - Using Device #0: AMD - Radeon RX 5500 XT

Issue description

When i set a big scene i want to preview to the Theme Editor, the contents gets cropped and i cannot use scrollbars or pan the view to see all the contents

Steps to reproduce

• Create a big scene, or use a small one with a big custom_minimum_size. You can also use https://github.com/godotengine/godot-demo-projects/blob/master/gui/control_gallery/control_gallery.tscn
• Create a new Theme and open the Theme Dock
• Press the + button to Add Preview and select your file or drag your scene next to it until you see a blue mark next to the Default Preview tab

Minimal reproduction project (MRP)

control gallery demo is a good fit.

https://github.com/godotengine/godot-demo-projects/tree/master/gui/control_gallery