Simplify builds' source repos

[Reinmar]

Two pain points:

• build-config.js vs src/ckeditor.js. I feel that leaving only the latter will make these repos easier to understand. It's a simple JS file, no magic there. Right now, we need to explain that you normally use build-config.js unless something. This is tricky and we've seen people doing mistakes because of that.
• Change the EditorClass.build's form to something clearer. First of all, the list of plugins there seems to be the same as config.plugins while it's not. Second, the build property is a bit unclear. Perhaps, we can merge this all into something like:

BalloonEditor.buildConfig = {
	availablePlugins: [
		EssentialsPlugin,
		UploadadapterPlugin,
		AutoformatPlugin,
		BoldPlugin,
		ItalicPlugin,
		BlockquotePlugin,
		EasyimagePlugin,
		HeadingPlugin,
		ImagePlugin,
		ImagecaptionPlugin,
		ImagestylePlugin,
		ImagetoolbarPlugin,
		ImageuploadPlugin,
		LinkPlugin,
		ListPlugin,
		ParagraphPlugin
	],
	toolbar: {
		items: [
			'heading',
			'|',
			'bold',
			'italic',
			'link',
			'bulletedList',
			'numberedList',
			'imageUpload',
			'blockQuote',
			'undo',
			'redo'
		]
	},
	image: {
		toolbar: [
			'imageStyle:full',
			'imageStyle:side',
			'|',
			'imageTextAlternative'
		]
	},
	language: 'en'
};

For comparison: https://github.com/ckeditor/ckeditor5-build-classic/blob/7e54c8d9f365a983d00fcf0da2102d761f37f7b6/build-config.js

[pjasiun]

Big 👍 from me. The current state is very misleading. I've already seen the wrong configuration because of it (someone put configuration option next to plugins).

[Reinmar]

Fun fact – the language: 'en' part of the current src/ckeditor.js wasn't necessary. Changing the setting of the CKEditor5WebpackPlugin() is enough. So, I confirmed we can remove build-config.js and avoid confusing duplication.

[ma2ciek]

Yes and no. If the only one language is provided, CKEditor5 will take that one. But if you feed CKEditor5 with many languages, then you need to specify which one should be loaded via the language option.

[Reinmar]

Are you sure? Cause I just checked :D

		new CKEditorWebpackPlugin( {
			// UI language. Language codes follow the https://en.wikipedia.org/wiki/ISO_639-1 format.
			// See: https://docs.ckeditor.com/ckeditor5/latest/features/ui-language.html
			language: 'en',
			additionalLanguages: 'all'
		} ),

With this configuration and no config.language passed to the editor, I can control the language by changing it in CKEditorWebpackPlugin().

[Reinmar]

Although, it may be a bit coincidental. And it works thanks to this:

	if ( numberOfLanguages === 1 ) {
		// Override the language to the only supported one.
		// This can't be done in the `Locale` class, because the translations comes after the `Locale` class initialization.
		language = Object.keys( window.CKEDITOR_TRANSLATIONS )[ 0 ];
	}

Still, editor.locale.language will always default to en. So you're right.

[Reinmar]

OK, there's a first PR: ckeditor/ckeditor5-build-classic#46

Please verify it before I'll update other repos.

PS. There's quite a lot of documentation to update now... ❤️

[Reinmar]

I know you won't read that so I'll repeat it here:

BTW, I was also thinking about Editor.builtinPlugins and Editor.builtinConfig which, at least for me, are more precise. I'm not sure, though, whether it isn't me only.

[Reinmar]

Part of the work is done in https://github.com/ckeditor/ckeditor5-core/issues/140. Tomorrow I'll remove build-config.js, createEntryFile() utils and do all the other changes. I'll have to review the docs too...

[Reinmar]

I merged code changes but I'm reopening because there's still documentation to be updated.