Add "preview_on_sphere" setting of material editor plugin

(cherry picked from commit 48b144afb7c91b1156e5aad091fd41de4eb88657)

editor/plugins/material_editor_plugin.cpp

@@ -94,6 +94,7 @@ void MaterialEditor::_button_pressed(Node *p_button) {
 		sphere_instance->hide();
 		box_switch->set_pressed(true);
 		sphere_switch->set_pressed(false);
+		EditorSettings::get_singleton()->set_project_metadata("inspector_options", "material_preview_on_sphere", false);
 	}
 
 	if (p_button == sphere_switch) {
@@ -101,6 +102,7 @@ void MaterialEditor::_button_pressed(Node *p_button) {
 		sphere_instance->show();
 		box_switch->set_pressed(false);
 		sphere_switch->set_pressed(true);
+		EditorSettings::get_singleton()->set_project_metadata("inspector_options", "material_preview_on_sphere", true);
 	}
 }
 
@@ -156,7 +158,6 @@ MaterialEditor::MaterialEditor() {
 	sphere_instance->set_mesh(sphere_mesh);
 	box_mesh.instance();
 	box_instance->set_mesh(box_mesh);
-	box_instance->hide();
 
 	set_custom_minimum_size(Size2(1, 150) * EDSCALE);
 
@@ -195,6 +196,15 @@ MaterialEditor::MaterialEditor() {
 	light_2_switch->connect("pressed", this, "_button_pressed", varray(light_2_switch));
 
 	first_enter = true;
+
+	if (EditorSettings::get_singleton()->get_project_metadata("inspector_options", "material_preview_on_sphere", true)) {
+		box_instance->hide();
+	} else {
+		box_instance->show();
+		sphere_instance->hide();
+		box_switch->set_pressed(true);
+		sphere_switch->set_pressed(false);
+	}
 }
 
 ///////////////////////