Split out VS Code reference provider from markdown reference provider (#152369)

This change renames the main markdown reference provider class to `MdReferenceComputer` and then uses this to implement a `vscode.ReferenceProvider`

This more cleanly splits the VS Code part of the logic from the general reference calculation stuff other providers consume

extensions/markdown-language-features/src/languageFeatures/definitionProvider.ts

@@ -5,16 +5,18 @@
 import * as vscode from 'vscode';
 import { Disposable } from '../util/dispose';
 import { SkinnyTextDocument } from '../workspaceContents';
-import { MdReferencesProvider } from './references';
+import { MdReferencesComputer } from './references';
 
 export class MdDefinitionProvider extends Disposable implements vscode.DefinitionProvider {
 
-	constructor(private readonly referencesProvider: MdReferencesProvider) {
+	constructor(
+		private readonly referencesComputer: MdReferencesComputer
+	) {
 		super();
 	}
 
 	async provideDefinition(document: SkinnyTextDocument, position: vscode.Position, token: vscode.CancellationToken): Promise<vscode.Definition | undefined> {
-		const allRefs = await this.referencesProvider.getAllReferencesAtPosition(document, position, token);
+		const allRefs = await this.referencesComputer.getReferencesAtPosition(document, position, token);
 
 		return allRefs.find(ref => ref.kind === 'link' && ref.isDefinition)?.location;
 	}