Private Properties phase 1 (#7666)

* Private Properties phase 1

Co-authored-by: CodingItWrong

* Private fields are optional

* Docs update

packages/babel-plugin-transform-parameters/src/rest.js

@@ -46,7 +46,7 @@ const memberExpressionOptimisationVisitor = {
     path.skip();
   },
 
-  "Function|ClassProperty": function(path, state) {
+  Function(path, state) {
     // Detect whether any reference to rest is contained in nested functions to
     // determine if deopt is necessary.
     const oldNoOptimise = state.noOptimise;