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/test/fixtures/assumption-ignoreFunctionLength/options.json

@@ -3,12 +3,14 @@
     "proposal-class-properties",
     "external-helpers",
     "syntax-flow",
-    ["transform-parameters", { "loose": true }],
+    "transform-parameters",
     "transform-block-scoping",
     "transform-spread",
     "transform-classes",
     "transform-destructuring",
-    "transform-arrow-functions",
-    "transform-for-of"
-  ]
+    "transform-arrow-functions"
+  ],
+  "assumptions": {
+    "ignoreFunctionLength": true
+  }
 }

packages/babel-plugin-transform-parameters/test/fixtures/loose/ignoreFunctionLength/input.js

@@ -0,0 +1,3 @@
+function fn(a, b = c()) {
+  return b;
+}

packages/babel-plugin-transform-parameters/test/fixtures/loose/ignoreFunctionLength/output.js

@@ -0,0 +1,7 @@
+function fn(a, b) {
+  if (b === void 0) {
+    b = c();
+  }
+
+  return b;
+}

packages/babel-plugin-transform-parameters/test/fixtures/loose/options.json

@@ -0,0 +1,5 @@
+{
+  "plugins": [
+    ["transform-parameters", { "loose": true }]
+  ]
+}