When clicking on a resource field in the inspector dock, you now have
the "Quick Load" option in addition to "Load". This opens a QuickOpen
dialog allowing the user to type in a phrase to quickly locate the
desired resource (similar to "Quick Open Scene").
In my experience, this is much faster than clicking through the File
Dialog.
Relates to godotengine/godot-proposals#346.
* LineEdit popups created on demand.
* TextEdit popups created on demand.
* SpinSlider popups created on demand.
* ResourcePicker popups created on demand.
Improves editor responsiveness.
