exports: also accept .js-suffixed deep imports

The exports map's './lib/*' pattern only covers bare deep imports
like require('rclnodejs/lib/distro'). Add a sibling './lib/*.js'
pattern so require('rclnodejs/lib/distro.js') resolves the same
file, instead of erroneously mapping to './lib/distro.js.js' and
throwing ERR_PACKAGE_PATH_NOT_EXPORTED.

Verified all forms now resolve: bare and .js-suffixed, top-level
and nested (lib/action/client[.js]).

Author: minggangw

package.json

@@ -15,6 +15,7 @@
     },
     "./rosocket": "./rosocket/index.js",
     "./lib/*": "./lib/*.js",
+    "./lib/*.js": "./lib/*.js",
     "./package.json": "./package.json"
   },
   "keywords": [