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-helper-wrap-function/src/index.js

@@ -57,7 +57,7 @@ function classOrObjectMethod(path: NodePath, callId: Object) {
     .unwrapFunctionEnvironment();
 }
 
-function plainFunction(path: NodePath, callId: Object) {
+function plainFunction(path: NodePath, callId: Object, noNewArrows: boolean) {
   const node = path.node;
   const isDeclaration = path.isFunctionDeclaration();
   const functionId = node.id;
@@ -68,7 +68,7 @@ function plainFunction(path: NodePath, callId: Object) {
     : buildAnonymousExpressionWrapper;
 
   if (path.isArrowFunctionExpression()) {
-    path.arrowFunctionToExpression();
+    path.arrowFunctionToExpression({ noNewArrows });
   }
 
   node.id = null;
@@ -123,10 +123,15 @@ function plainFunction(path: NodePath, callId: Object) {
   }
 }
 
-export default function wrapFunction(path: NodePath, callId: Object) {
+export default function wrapFunction(
+  path: NodePath,
+  callId: Object,
+  // TODO(Babel 8): Consider defaulting to false for spec compliancy
+  noNewArrows: boolean = true,
+) {
   if (path.isMethod()) {
     classOrObjectMethod(path, callId);
   } else {
-    plainFunction(path, callId);
+    plainFunction(path, callId, noNewArrows);
   }
 }