[IMP] reactivity: replace sets with small arrays for performance

While Sets have better lookup complexity than arrays, because of the
large constant factors, small arrays can perform better than small sets
when checking for inclusion.

In practice, replacing both of the raw types sets with arrays can
improve performance of reactive-heavy workloads by as much as 30%.

Considering the reactivity code is very hot when rendering data-heavy
components, and the low impact on readability of the fix, the
cost-benefit analysis is clearly in favour of making the fix.

src/runtime/reactivity.ts

@@ -20,8 +20,9 @@ type CollectionRawType = "Set" | "Map" | "WeakMap";
 const objectToString = Object.prototype.toString;
 const objectHasOwnProperty = Object.prototype.hasOwnProperty;
 
-const SUPPORTED_RAW_TYPES = new Set(["Object", "Array", "Set", "Map", "WeakMap"]);
-const COLLECTION_RAWTYPES = new Set(["Set", "Map", "WeakMap"]);
+// Use arrays because Array.includes is faster than Set.has for small arrays
+const SUPPORTED_RAW_TYPES = ["Object", "Array", "Set", "Map", "WeakMap"];
+const COLLECTION_RAW_TYPES = ["Set", "Map", "WeakMap"];
 
 /**
  * extract "RawType" from strings like "[object RawType]" => this lets us ignore
@@ -45,7 +46,7 @@ function canBeMadeReactive(value: any): boolean {
   if (typeof value !== "object") {
     return false;
   }
-  return SUPPORTED_RAW_TYPES.has(rawType(value));
+  return SUPPORTED_RAW_TYPES.includes(rawType(value));
 }
 /**
  * Creates a reactive from the given object/callback if possible and returns it,
@@ -220,7 +221,7 @@ export function reactive<T extends Target>(target: T, callback: Callback = NO_CA
   const reactivesForTarget = reactiveCache.get(target)!;
   if (!reactivesForTarget.has(callback)) {
     const targetRawType = rawType(target);
-    const handler = COLLECTION_RAWTYPES.has(targetRawType)
+    const handler = COLLECTION_RAW_TYPES.includes(targetRawType)
       ? collectionsProxyHandler(target as Collection, callback, targetRawType as CollectionRawType)
       : basicProxyHandler<T>(callback);
     const proxy = new Proxy(target, handler as ProxyHandler<T>) as Reactive<T>;