First cut at unifying notebook renderers apis

This implements the api described in #123540. Major points:

- Instead of having the `markdown-it` renderer pull it its dependencies, instead the dependencies can call `getRenderer` to import the object returned by the `markdown-it` renderer

- We try to detect if a renderer is using the old or new api. Old renderers are still run as globals while new ones are loaded with `import`

- I have only hooked up the new API for markdown renderers so far

extensions/markdown-language-features/notebook/index.ts

@@ -5,35 +5,23 @@
 
 const MarkdownIt = require('markdown-it');
 
-export async function activate(ctx: {
-	dependencies: ReadonlyArray<{ entrypoint: string }>
-}) {
+export function activate() {
 	let markdownIt = new MarkdownIt({
 		html: true
 	});
 
-	// Should we load the deps before this point?
-	// Also could we await inside `renderMarkup`?
-	await Promise.all(ctx.dependencies.map(async (dep) => {
-		try {
-			const api = await import(dep.entrypoint);
-			if (api?.extendMarkdownIt) {
-				markdownIt = api.extendMarkdownIt(markdownIt);
-			}
-		} catch (e) {
-			console.error('Could not load markdown entryPoint', e);
-		}
-	}));
-
 	return {
-		renderMarkup: (context: { element: HTMLElement, content: string }) => {
-			const rendered = markdownIt.render(context.content);
+		renderCell: (_id: string, context: { element: HTMLElement, value: string }) => {
+			const rendered = markdownIt.render(context.value);
 			context.element.innerHTML = rendered;
 
 			// Insert styles into markdown preview shadow dom so that they are applied
 			for (const markdownStyleNode of document.getElementsByClassName('markdown-style')) {
 				context.element.insertAdjacentElement('beforebegin', markdownStyleNode.cloneNode(true) as Element);
 			}
+		},
+		extendMarkdownIt: (f: (md: typeof markdownIt) => void) => {
+			f(markdownIt);
 		}
 	};
 }