Breaking: Use named exports in metro-babel-register

Summary:
X-link: react/react-native#52564

Currently, `metro-babel-register` has a function as its default export, to which we've tagged on various properties.

This tidies that up to a more idiomatic object of named exports, with `register` as a new one of them.

This also serves to make it more compatible with automatic TypeScript generation.

This is semver breaking, but `metro-babel-register` has very little usage outside Meta projects so isn't expected to be disruptive.

Changelog: [Internal]

Metro changelog:
```
 - **[Breaking]**: Move metro-babel-register's main function to a named export `register`
```

Reviewed By: huntie

Differential Revision: D78157559

fbshipit-source-id: c59c9820e9895007345561fed9ccec2273b925c8

Author: robhogan

packages/metro-babel-register/src/babel-register.js

@@ -181,8 +181,9 @@ function registerForMetroMonorepo() {
   isRegisteredForMetroMonorepo = true;
 }
 
-register.config = config;
-register.buildRegExps = buildRegExps;
-register.unstable_registerForMetroMonorepo = registerForMetroMonorepo;
-
-module.exports = register;
+module.exports = {
+  register,
+  config,
+  buildRegExps,
+  unstable_registerForMetroMonorepo: registerForMetroMonorepo,
+};