feat: reduce unnecessary exports runtime

[fi3ework]

What kind of change does this PR introduce?

The initial goal of this PR is to reduce unnecessary runtime code in modern-module. As __webpack_exports__ and related define property runtime is not needed.

Contains following changes:

1. Explicit define RuntimeGlobals.exports instead of using the always pre-rendered __webpack_exports__ in source, only render it when runtime requirements exist.

   • where RuntimeGlobals.onChunksLoaded is added, also adding RuntimeGlobals.exports
   • Add RuntimeGlobals.exports to lib/library/AssignLibraryPlugin.js and lib/library/ExportPropertyLibraryPlugin.js to inherit the explicit defined RuntimeGlobals.exports runtime.

2. Do not render RuntimeGlobals.exports & RuntimeGlobals.definePropertyGetters in modern-module mode.

Did you add tests for your changes?

Yes.

Does this PR introduce a breaking change?

I don't think so. __webpack_exports__ is striped only when is useless.

What needs to be documented once your changes are merged?

No.

[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)