SyntaxError is not thrown, while parsing ESM with multiple default exports

While working on the QTBUG-117849 it was discovered that Neither Parser nor JSEngine throw a SyntaxError when parsing / importing ESM containing multiple default exports.

https://codereview.qt-project.org/c/qt/qtdeclarative/+/547817

SyntaxError should be thrown acc. to the standard

 The duplicate ExportedNames rule implies that multiple export default ExportDeclaration items within a ModuleBody is a Syntax Error. 

https://262.ecma-international.org/7.0/#sec-module-semantics-static-semantics-early-errors