Implement camera orbiting shortcuts.

Fixes godotengine/godot-proposals#2051.
Relates to godotengine/godot-proposals#1215.

Implements shortucts for adjusting the camera rotation in 15-degree
increments, similar to Blender.

I did not add corresponding menu entries for these, as I didn't feel
like they would be too useful from a menu, and didn't want to make the
menu too long.

(cherry picked from commit cb15ec20bbbac56014b84169507eed323786f596)

editor/plugins/spatial_editor_plugin.cpp

@@ -2042,6 +2042,21 @@ void SpatialEditorViewport::_sinput(const Ref<InputEvent> &p_event) {
 		if (ED_IS_SHORTCUT("spatial_editor/right_view", p_event)) {
 			_menu_option(VIEW_RIGHT);
 		}
+		if (ED_IS_SHORTCUT("spatial_editor/orbit_view_down", p_event)) {
+			cursor.x_rot -= Math_PI / 12.0;
+		}
+		if (ED_IS_SHORTCUT("spatial_editor/orbit_view_up", p_event)) {
+			cursor.x_rot += Math_PI / 12.0;
+		}
+		if (ED_IS_SHORTCUT("spatial_editor/orbit_view_right", p_event)) {
+			cursor.y_rot -= Math_PI / 12.0;
+		}
+		if (ED_IS_SHORTCUT("spatial_editor/orbit_view_left", p_event)) {
+			cursor.y_rot += Math_PI / 12.0;
+		}
+		if (ED_IS_SHORTCUT("spatial_editor/orbit_view_180", p_event)) {
+			cursor.y_rot += Math_PI;
+		}
 		if (ED_IS_SHORTCUT("spatial_editor/focus_origin", p_event)) {
 			_menu_option(VIEW_CENTER_TO_ORIGIN);
 		}
@@ -6460,6 +6475,11 @@ SpatialEditor::SpatialEditor(EditorNode *p_editor) {
 	ED_SHORTCUT("spatial_editor/front_view", TTR("Front View"), KEY_KP_1);
 	ED_SHORTCUT("spatial_editor/left_view", TTR("Left View"), KEY_MASK_ALT + KEY_KP_3);
 	ED_SHORTCUT("spatial_editor/right_view", TTR("Right View"), KEY_KP_3);
+	ED_SHORTCUT("spatial_editor/orbit_view_down", TTR("Orbit View Down"), KEY_KP_2);
+	ED_SHORTCUT("spatial_editor/orbit_view_left", TTR("Orbit View Left"), KEY_KP_4);
+	ED_SHORTCUT("spatial_editor/orbit_view_right", TTR("Orbit View Right"), KEY_KP_6);
+	ED_SHORTCUT("spatial_editor/orbit_view_up", TTR("Orbit View Up"), KEY_KP_8);
+	ED_SHORTCUT("spatial_editor/orbit_view_180", TTR("Orbit View 180"), KEY_KP_9);
 	ED_SHORTCUT("spatial_editor/switch_perspective_orthogonal", TTR("Switch Perspective/Orthogonal View"), KEY_KP_5);
 	ED_SHORTCUT("spatial_editor/insert_anim_key", TTR("Insert Animation Key"), KEY_K);
 	ED_SHORTCUT("spatial_editor/focus_origin", TTR("Focus Origin"), KEY_O);