feat: support dragging resources to the resource-picker

This extends the resource-picker to support a simple drag-and-drop from
the FileSystem tab.

The resource_picker's line_edit's MouseFilter was set to 'pass' so the
drag/drop input could live on the resource_picker itself, which was a
bit simpler than extending a custom LineEdit component.

addons/pandora/ui/components/resource_picker/resource_picker.gd

@@ -34,3 +34,13 @@ func _path_changed(new_path:String) -> void:
 			resource_changed.emit(new_path)
 		else:
 			line_edit.text = resource_path
+
+func _can_drop_data(_pos, data):
+	if data.type == "files":
+		return true
+	return false
+
+func _drop_data(_pos, data):
+	if data.type == "files":
+		var path = data.files[0]
+		_path_changed(path)

addons/pandora/ui/components/resource_picker/resource_picker.tscn

@@ -11,6 +11,7 @@ script = ExtResource("1_hjkiw")
 [node name="LineEdit" type="LineEdit" parent="."]
 layout_mode = 2
 size_flags_horizontal = 3
+mouse_filter = 1
 
 [node name="LoadFileButton" type="Button" parent="."]
 layout_mode = 2