Implement assumptions defined in the babel/rfcs#5 RFC

- `mutableTemplateObject` and `ignoreToPrimitiveHint` (#12408)
- `setClassMethods` (#12407)
- `setComputedProperties` (#12490)
- `ignoreFunctionLength` (#12491)
- `noDocumentAll` (#12481)
- `iterableIsArray` and `arrayLikeIsIterable` (#12489)
- `pureGetters` (#12504)
- `skipForOfIteratorClosing` (#12496)
- `objectRestNoSymbols`, `setSpreadProperties` and `pureGetters` (#12505)
- `noNewArrows` (#12613, #12793)
- `setPublicClassFields` and `privateFieldsAsProperties` (#12497)
- `constantReexports` and `enumerableModuleMeta` (#12618)
- `constantSuper`, `superIsCallableConstructor` and `noClassCalls` (#12726)

Co-authored-by: Justin Ridgewell <justin@ridgewell.name>
Co-authored-by: Huáng Jùnliàng <JLHwung@users.noreply.github.com>

packages/babel-plugin-transform-spread/src/index.js

@@ -5,13 +5,18 @@ import { types as t } from "@babel/core";
 export default declare((api, options) => {
   api.assertVersion(7);
 
-  const { loose, allowArrayLike } = options;
+  const iterableIsArray = api.assumption("iterableIsArray") ?? options.loose;
+  const arrayLikeIsIterable =
+    options.allowArrayLike ?? api.assumption("arrayLikeIsIterable");
 
   function getSpreadLiteral(spread, scope) {
-    if (loose && !t.isIdentifier(spread.argument, { name: "arguments" })) {
+    if (
+      iterableIsArray &&
+      !t.isIdentifier(spread.argument, { name: "arguments" })
+    ) {
       return spread.argument;
     } else {
-      return scope.toArray(spread.argument, true, allowArrayLike);
+      return scope.toArray(spread.argument, true, arrayLikeIsIterable);
     }
   }