feat(language-core): reimplement multi-source mapping

[johnsoncodehk]

c4b297b removed multi-source support, but to support Angular use cases, this PR re-implements it.

Changes

• getAssociatedScript needs to be called to explicitly register dependencies on additional sources.
• Mappings with additional source scripts should be added to associatedScriptMappings instead of using the Mapping#source field.
• The Mapping#source field has beed removed.

Example:

export const angularLanguagePlugin: LanguagePlugin<string> = {
	createVirtualCode(fileName, languageId, snapshot, { getAssociatedScript }) {
		if (fileName.endsWith('app.component.ts')) {

			// Register dependencies
			const templateScript = getAssociatedScript('.../template.html');

			if (templateScript) {
				return {
					mappings: [
						// Mappings for app.component.ts
					],
					associatedScriptMappings: new Map([
						[templateScript.id, [
							// Mappings for template.html
						]],
					])
				}
			}
		}
	},
};

[johnsoncodehk]

In fact I'm not sure if "associated" is a better term than "related".

[piotrtomiak]

@johnsoncodehk - thanks for taking a look at this so quickly! I am now trying to rebase my changes on top of these changes.

[piotrtomiak]

@johnsoncodehk - I've finally managed to rebase the changes. It took more, because I as off most of yesterday. The PR is here: #197