Make sun energy adjustable as a float in the 3D editor's preview sun

(cherry picked from commit 5e1cb39101a20b58d3ea7ec8e2f2124c1b04e0fa)

editor/plugins/node_3d_editor_plugin.cpp

@@ -8545,9 +8545,11 @@ void fragment() {
 		sun_color->get_popup()->connect("about_to_popup", callable_mp(EditorNode::get_singleton(), &EditorNode::setup_color_picker).bind(sun_color->get_picker()));
 
 		sun_energy = memnew(EditorSpinSlider);
+		sun_energy->set_max(64.0);
+		sun_energy->set_min(0);
+		sun_energy->set_step(0.05);
 		sun_vb->add_margin_child(TTR("Sun Energy"), sun_energy);
 		sun_energy->connect("value_changed", callable_mp(this, &Node3DEditor::_preview_settings_changed).unbind(1));
-		sun_energy->set_max(64.0);
 
 		sun_max_distance = memnew(EditorSpinSlider);
 		sun_vb->add_margin_child(TTR("Shadow Max Distance"), sun_max_distance);