Fix private property parsing in Flow (#8340)

* Fix private property parsing in Flow

* Flow tests updated

* Fix type error

* Appropriate name was given to test folder

* Fix

* Empty

* Correct type annotation

* Add required changes in generator package

* Add required changes in flow-strip-types

packages/babel-parser/src/plugins/flow.js

@@ -1917,6 +1917,15 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       return super.parseClassProperty(node);
     }
 
+    parseClassPrivateProperty(
+      node: N.ClassPrivateProperty,
+    ): N.ClassPrivateProperty {
+      if (this.match(tt.colon)) {
+        node.typeAnnotation = this.flowParseTypeAnnotation();
+      }
+      return super.parseClassPrivateProperty(node);
+    }
+
     // determine whether or not we're currently in the position where a class method would appear
     isClassMethod(): boolean {
       return this.isRelational("<") || super.isClassMethod();

packages/babel-parser/src/types.js

@@ -717,6 +717,7 @@ export type ClassPrivateProperty = NodeBase & {
   value: ?Expression, // TODO: Not in spec that this is nullable.
   static: boolean,
   computed: false,
+  typeAnnotation?: ?TypeAnnotation, // TODO: Not in spec
 };
 
 export type OptClassDeclaration = ClassBase &