build(deps): upgrade to TypeScript 4

packages/runtime-core/src/apiCreateApp.ts

@@ -258,7 +258,7 @@ export function createAppAPI<HostElement>(
       },
 
       provide(key, value) {
-        if (__DEV__ && key in context.provides) {
+        if (__DEV__ && (key as string | symbol) in context.provides) {
           warn(
             `App already provides property with key "${String(key)}". ` +
               `It will be overwritten with the new value.`

packages/runtime-core/src/apiInject.ts

@@ -37,7 +37,7 @@ export function inject(
   const instance = currentInstance || currentRenderingInstance
   if (instance) {
     const provides = instance.provides
-    if (key in provides) {
+    if ((key as string | symbol) in provides) {
       // TS doesn't allow symbol as index type
       return provides[key as string]
     } else if (arguments.length > 1) {