extensions/markdown-language-features/src/commandManager.ts/CommandManager/registerCommand
class CommandManager:	private registerCommand(id: string, impl: (...args: any[]) => void, thisArg?: any) {
		if (this.commands.has(id)) {
			return;
		}

		this.commands.set(id, vscode.commands.registerCommand(id, impl, thisArg));
	}