Move DLL definition to main CKEditor5 package.

[jodator]

Suggested merge commit message (convention)

Internal: Move DLL definition to main CKEditor5 package. Closes #8578.

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Additional information

This PR adds a meaning to the ckeditor5 package 😉

AFICS this setup works:

1. The ckeditor5 package has src dir with public-public API of base/core CKEditor5 packages as identified in the Implement DLLs for CKEditor 5 features #8517 task. So ckeditor5-core re-exports are in src/core.js file.
2. The dependant plugin, verified with BasicStyles package, defines dependency as: ckeditor5: "^23.1.0" .
3. The webpack.dll.config is simpler now and has only one entry:

new webpack.DllReferencePlugin( {
	manifest: require( '../../build/ckeditor5-dll.manifest.json' ),
	scope: 'ckeditor5/src'
} )

AFAICS the yarn install worked.

[jodator]

@ckeditor/qa-team  I'll be working on this a bit more to verify other packages. But for now, could you also verify that it works for you?

1. Please use clean install (no previous node_modules).
2. Do yarn install as normal.
3. Run yarn run build:dll task in the main folder.
4. Run webpack in ckeditor5/sample/plugin folder.
5. Open the ckeditor5/sample/index.html in the browser.

If the plugins HtmlEmbed and Image fail, please remove them from the sample index.html.

It should work OK with all the packages in the sample.

[jodator]

@pomek please take a look at this as it might invalidate your task about automation. At least in some sort.

[pomek]

LGTM.