Possibly add external dependencies on the last chunk only

[swashata]

Multiple entry-points from the same files entry have common dependency.

Now one of the entry point may depend on say wp-blocks, but not the other. In this
case with current approach, we add wp-blocks to every entry chunks, including runtime, vendor etc.

So depending on which entry-point we have called first, additional external WordPress dependencies might come to the page where it shouldn't.

To solve this, we can

1. Split files entry through multi-compiler mode where we know that none of them share anything common.
2. Or just add the external WP dependencies to the last chunk of an entry-point.

I am not sure if 2 should be a good approach here. Because in theory, the vendor could have external dependency too.