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-parameters/src/params.js

@@ -44,7 +44,7 @@ const iifeVisitor = {
 // last 2 parameters are optional -- they are used by proposal-object-rest-spread/src/index.js
 export default function convertFunctionParams(
   path,
-  loose,
+  ignoreFunctionLength,
   shouldTransformParam,
   replaceRestElement,
 ) {
@@ -123,7 +123,10 @@ export default function convertFunctionParams(
     }
 
     const paramIsAssignmentPattern = param.isAssignmentPattern();
-    if (paramIsAssignmentPattern && (loose || node.kind === "set")) {
+    if (
+      paramIsAssignmentPattern &&
+      (ignoreFunctionLength || node.kind === "set")
+    ) {
       const left = param.get("left");
       const right = param.get("right");
 
@@ -203,6 +206,8 @@ export default function convertFunctionParams(
     // sure that we correctly handle this and arguments.
     const bodyPath = path.get("body.body");
     const arrowPath = bodyPath[bodyPath.length - 1].get("argument.callee");
+
+    // This is an IIFE, so we don't need to worry about the noNewArrows assumption
     arrowPath.arrowFunctionToExpression();
 
     arrowPath.node.generator = path.node.generator;