[INTERNAL] lib/processors/jsdoc: function result union needs parentheses

Otherwise this function which returns either an object or null:
@returns {function(sap.ui.core.Control): ({rows: int, columns:
int}|null)|undefined}

ends up as:
function(sap.ui.core.Control):{rows: int, columns: int} | null |
undefined

Which means the function *always* has an object as result and there
could be null or undefined as *alternative* to the function.

Cherry picked from SAP/openui5@b21d5c95c.

lib/processors/jsdoc/lib/ui5/plugin.cjs

@@ -3164,13 +3164,19 @@ exports.astNodeVisitor = {
 					typeString += `(${paramTypes.join(", ")})`;
 				}
 				if (parsedType.result) {
-					typeString += `:${toTypeString(parsedType.result)}`;
+					let resultType = toTypeString(parsedType.result);
+					// ensure the function result remains belonging together even when a union of the entire function with other types is created
+					// Example: ensure parentheses around function result in:  function(int):({rows: int, columns: int}|null)|undefined
+					if (parsedType.result.type === "TypeUnion") {
+						resultType = `(${resultType})`;
+					}
+					typeString += `:${resultType}`;
 				}
 				types.push(typeString);
 				// #### END: MODIFIED BY SAP
 				break;
 			 case TYPES.NameExpression:
-				 types.push(parsedType.name);
+				types.push(parsedType.name);
 				break;
 			case TYPES.NullLiteral:
 				types.push('null');