src/vs/workbench/contrib/terminal/browser/terminalService.ts/TerminalService/_handleInstanceContextKeys
class TerminalService:	private _handleInstanceContextKeys(): void {
		const terminalIsOpenContext = TerminalContextKeys.isOpen.bindTo(this._contextKeyService);
		const updateTerminalContextKeys = () => {
			terminalIsOpenContext.set(this.instances.length > 0);
			this._terminalCountContextKey.set(this.instances.length);
		};
		this.onDidChangeInstances(() => updateTerminalContextKeys());
	}