Clean up structure of markdown extension (#161148)

- Move things related to the client under `client`
- Remove extra abstractions that are no longer used
- Add MdLanguageClient type

extensions/markdown-language-features/src/client/protocol.ts

@@ -0,0 +1,38 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import type Token = require('markdown-it/lib/token');
+import * as vscode from 'vscode';
+import { RequestType } from 'vscode-languageclient';
+import type * as lsp from 'vscode-languageserver-types';
+import type * as md from 'vscode-markdown-languageservice';
+
+
+export type ResolvedDocumentLinkTarget =
+	| { readonly kind: 'file'; readonly uri: vscode.Uri; position?: lsp.Position; fragment?: string }
+	| { readonly kind: 'folder'; readonly uri: vscode.Uri }
+	| { readonly kind: 'external'; readonly uri: vscode.Uri };
+
+//#region From server
+export const parse = new RequestType<{ uri: string }, Token[], any>('markdown/parse');
+
+export const fs_readFile = new RequestType<{ uri: string }, number[], any>('markdown/fs/readFile');
+export const fs_readDirectory = new RequestType<{ uri: string }, [string, { isDirectory: boolean }][], any>('markdown/fs/readDirectory');
+export const fs_stat = new RequestType<{ uri: string }, { isDirectory: boolean } | undefined, any>('markdown/fs/stat');
+
+export const fs_watcher_create = new RequestType<{ id: number; uri: string; options: md.FileWatcherOptions; watchParentDirs: boolean }, void, any>('markdown/fs/watcher/create');
+export const fs_watcher_delete = new RequestType<{ id: number }, void, any>('markdown/fs/watcher/delete');
+
+export const findMarkdownFilesInWorkspace = new RequestType<{}, string[], any>('markdown/findMarkdownFilesInWorkspace');
+//#endregion
+
+//#region To server
+export const getReferencesToFileInWorkspace = new RequestType<{ uri: string }, lsp.Location[], any>('markdown/getReferencesToFileInWorkspace');
+export const getEditForFileRenames = new RequestType<Array<{ oldUri: string; newUri: string }>, lsp.WorkspaceEdit, any>('markdown/getEditForFileRenames');
+
+export const fs_watcher_onChange = new RequestType<{ id: number; uri: string; kind: 'create' | 'change' | 'delete' }, void, any>('markdown/fs/watcher/onChange');
+
+export const resolveLinkTarget = new RequestType<{ linkText: string; uri: string }, ResolvedDocumentLinkTarget, any>('markdown/resolveLinkTarget');
+//#endregion