Can't create a new material by dragging a shader on user-exported properties if they're not *specifically* ShaderMaterials

[mieldepoche]

Godot version

4.1.1

System information

linux

Issue description

simplescreenrecorder-2023-09-16_07.31.44.webm

as you can see, I can't automatically create a new ShaderMaterial by dropping a shader on a material slot when the material slot is one I exported from a script, unless I set the export type to ShaderMaterial specifically (not showcased in video).

Steps to reproduce

@export var wont_work: Material
@export var will_work: ShaderMaterial

and then drop a Shader resource on both of those in the inspector.

Minimal reproduction project

the script above and an empty .gdshader file

[jsjtxietian]

Is this expected or a bug?

The export property's base_type in editor_resource_picker is Material for won't work and ShaderMaterial for will work, but the
GeometryInstance3D's material field's base_type is BaseMaterial3D,ShaderMaterial.

And in _get_allowed_types , for a ShaderMaterial, it will insert a Shader to allowed_types, but for Material it won't do so. That's why we can't drag a shader directly to the exported material property.

godot/editor/editor_resource_picker.cpp

Lines 624 to 632 in 571cd0e

	if (p_with_convert) {
	if (base == "BaseMaterial3D") {
	p_vector->insert("Texture2D");
	} else if (base == "ShaderMaterial") {
	p_vector->insert("Shader");
	} else if (base == "Texture2D") {
	p_vector->insert("Image");
	}
	}

For a quick fix, we can insert a Shader to allowed_types for Material too. But it might have some unexpected behaviour. Any ideas?