extensions/markdown-language-features/src/markdownEngine.ts/MarkdownEngine/addLineNumberRenderer
class MarkdownEngine:	private addLineNumberRenderer(md: MarkdownIt, ruleName: string): void {
		const original = md.renderer.rules[ruleName];
		md.renderer.rules[ruleName] = (tokens: Token[], idx: number, options: any, env: any, self: any) => {
			const token = tokens[idx];
			if (token.map && token.map.length) {
				token.attrSet('data-line', token.map[0] + '');
				token.attrJoin('class', 'code-line');
			}

			if (original) {
				return original(tokens, idx, options, env, self);
			} else {
				return self.renderToken(tokens, idx, options, env, self);
			}
		};
	}