fix(ui5-tooling-modules): support 'as default' exports in modules

[petermuessig]

This is e.g. the case in the fetch-mock module:

[...]

var index = FetchMock.createInstance();

export { index as default };

This then returns an object having a default property but it isn't detected properly by rollup. The __esModule support ensures to also get access to the default property at the import.