fix and test module federation with ESM

[sokra]

This fixes the problems when using:

experiments: {
	outputModule: true
},
plugins: [
	new ModuleFederationPlugin({
		library: { type: "module" },
		...

What kind of change does this PR introduce?
bugfix

Did you add tests for your changes?
yes

Does this PR introduce a breaking change?
no

What needs to be documented once your changes are merged?
nothing

[webpack-bot]

For maintainers only:

• This needs to be documented (issue in webpack/webpack.js.org will be filed when merged)
• This needs to be backported to webpack 4 (issue will be created when merged)