Private class methods stage 3 (#8654)

* Add private method syntax support

* Add private method spec support

* Add private method loose support

* Throw error if static private method is used

* Add more isStatic & isMethod checks

* Remove `writable:false` from private method inits

`writable` is false by default.

* Add private method func obj equality check

* Throw if private accessor is used

* Add check for fields === private method loose mode

* Throw buildCodeFrameErrors instead of Errors

* Move obj destructuring inside for loop

* Remove "computed" from ClassPrivateMethod type def

packages/babel-plugin-proposal-private-methods/src/index.js

@@ -0,0 +1,25 @@
+import { declare } from "@babel/helper-plugin-utils";
+import pluginClassFeatures, {
+  enableFeature,
+  FEATURES,
+} from "@babel/plugin-class-features";
+
+export default declare((api, options) => {
+  api.assertVersion(7);
+
+  const { loose } = options;
+
+  return {
+    name: "proposal-private-methods",
+
+    inherits: pluginClassFeatures,
+
+    manipulateOptions(opts, parserOpts) {
+      parserOpts.plugins.push("classPrivateMethods");
+    },
+
+    pre() {
+      enableFeature(this.file, FEATURES.privateMethods, loose);
+    },
+  };
+});