Reduce recomputation of state in markdown extension (#152804)

* Reduce recomputation of state in markdown extension

- Use `getForDocument` more often to avoid refetching documents
- Debounce `MdTableOfContentsWatcher`. We don't want this to trigger on every keystroke :)

* Cache LinkDefinitionSet

* Add test file change

* Fix toc watcher for tests

extensions/markdown-language-features/src/markdownEngine.ts

@@ -6,13 +6,14 @@
 import type MarkdownIt = require('markdown-it');
 import type Token = require('markdown-it/lib/token');
 import * as vscode from 'vscode';
-import { MdDocumentInfoCache } from './util/workspaceCache';
+import { ILogger } from './logging';
 import { MarkdownContributionProvider } from './markdownExtensions';
 import { Slugifier } from './slugify';
 import { Disposable } from './util/dispose';
 import { stringHash } from './util/hash';
 import { WebviewResourceProvider } from './util/resources';
 import { isOfScheme, Schemes } from './util/schemes';
+import { MdDocumentInfoCache } from './util/workspaceCache';
 import { MdWorkspaceContents, SkinnyTextDocument } from './workspaceContents';
 
 const UNICODE_NEWLINE_REGEX = /\u2028|\u2029/g;
@@ -95,6 +96,7 @@ interface RenderEnv {
 
 export interface IMdParser {
 	readonly slugifier: Slugifier;
+
 	tokenize(document: SkinnyTextDocument): Promise<Token[]>;
 }
 
@@ -110,6 +112,7 @@ export class MarkdownItEngine implements IMdParser {
 	public constructor(
 		private readonly contributionProvider: MarkdownContributionProvider,
 		slugifier: Slugifier,
+		private readonly logger: ILogger,
 	) {
 		this.slugifier = slugifier;
 
@@ -180,6 +183,7 @@ export class MarkdownItEngine implements IMdParser {
 			return cached;
 		}
 
+		this.logger.verbose('MarkdownItEngine', `tokenizeDocument - ${document.uri}`);
 		const tokens = this.tokenizeString(document.getText(), engine);
 		this._tokenCache.update(document, config, tokens);
 		return tokens;