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-destructuring/test/fixtures/assumption-iterableIsArray/basic/input.js

@@ -0,0 +1 @@
+let [foo, bar] = baz;

packages/babel-plugin-transform-destructuring/test/fixtures/assumption-iterableIsArray/basic/output.js

@@ -0,0 +1,3 @@
+let _baz = baz,
+    foo = _baz[0],
+    bar = _baz[1];

packages/babel-plugin-transform-destructuring/test/fixtures/assumption-iterableIsArray/for-in/input.js

@@ -0,0 +1,7 @@
+for (var [name, value] in obj) {
+  print("Name: " + name + ", Value: " + value);
+}
+
+for ([name, value] in obj) {
+  print("Name: " + name + ", Value: " + value);
+}

packages/babel-plugin-transform-destructuring/test/fixtures/assumption-iterableIsArray/for-in/output.js

@@ -0,0 +1,11 @@
+for (var _ref in obj) {
+  var name = _ref[0];
+  var value = _ref[1];
+  print("Name: " + name + ", Value: " + value);
+}
+
+for (var _ref2 in obj) {
+  name = _ref2[0];
+  value = _ref2[1];
+  print("Name: " + name + ", Value: " + value);
+}

packages/babel-plugin-transform-destructuring/test/fixtures/assumption-iterableIsArray/options.json

@@ -0,0 +1,9 @@
+{
+  "plugins": [
+    ["external-helpers", { "helperVersion": "7.100.0" }],
+    "transform-destructuring"
+  ],
+  "assumptions": {
+    "iterableIsArray": true
+  }
+}