fix: add missing package.json and source maps (#5040)

* Use --exclude to skip node_modules

Instead of copying and then deleting them.  This will also catch some
node_modules directories that were missed.

* Remove per-extension dependency install

Code packages all the dependencies using webpack for each extension so
there are no dependencies to install.

* Include source maps

I also moved this to its own patch because it feels sufficiently
standalone.

Fixes #5026.

* Refresh language patch

The base is slightly different so it needed to be refreshed.

* Add missing package.json

This was caused by switching to Code's package step which does not
include the package.json.

Fixes #5019.

* Include keytar

It seems this actually is used now.