`PrivateName` should be migrated to `PrivateIdentifier`

[btiernay]

Per the ESTree specification, PrivateName should should be PrivateIdentifier

This will ensure interoperability with other parsers such as esprima-next. Currently the following pre-walk of the raw AST is required:

            // We need to fix the AST to match the expected format of recast (i.e. ast-types)
            const vistitor = new class extends Visitor {
                visitPrivateIdentifier(node) {
                    node.type = 'PrivateName'
                    return super.visitPrivateIdentifier(node);
                }
            }

            vistitor.visit(ast);

See estree/estree#240 for further details.