Simplify `_.slice`.
Add more placeholder tests.
Pass the converted `iterable` to the `iterator` instead of the `collection`.
Remove unneeded branch of `_.slice`.
Make `_.parseInt` work as a callback to `_.map`.
Make `_.random` and `_.range` work as callbacks to `_.map`.
Add `guard` param doc to `_.parseInt`. [ci skip]
Fix placeholder support without metadata.
Comma and whitespace nits. [ci skip]
Ensure `EXPANDO` doesn't disable fast properties in v8.