Add heatmap for vega lite demo

packages/core/src/components/stores.ts

@@ -1,3 +1,3 @@
 import { writable } from 'svelte/store'
 import { VisahoiState } from './state'
-export const stores = writable<Map<string, VisahoiState>>(new Map())
+export const stores = writable<Map<string, VisahoiState>>(new Map())