I always found the `resolve_if_necessary` method pretty confusing
because by reading it, it suggests that resolution always happens, and
the point is whether that needs to be local or remote. This commit tries
to make that more clear.

https://github.com/rubygems/rubygems/commit/93d6861ee8

All we need is to setup remote or local sources appropriately.

https://github.com/rubygems/rubygems/commit/3ceff46a2a

There seems to be no reason why the install should be serial for --local.
The packages are still installed in the right dependency order in this case, so that parallel install can be used.
This patch disables parallel install only in case of no_install_needed.

Also remove the `option` argument, which is effectifely not used.

https://github.com/rubygems/rubygems/commit/5da934ddb6

https://github.com/rubygems/rubygems/commit/b9a2d4d539

Removes an (in my opinion) excessive indirection and handles options
more consistently.

https://github.com/rubygems/rubygems/commit/642e6d2c0c

https://github.com/rubygems/rubygems/commit/7ddf1dc70a

If Gemfile is empty and there's no lockfile (situation after `bundle init`), and
`frozen` is configured, running `bundle add` will result in an strange
error, like this:

```
$ bundle add rake
, but the lockfile can't be updated because frozen mode is set

You have deleted from the Gemfile:
* rake (~> 13.2)

Run `bundle install` elsewhere and add the updated Gemfile to version control.
```

This commit fixes the problem to instead print

https://github.com/rubygems/rubygems/commit/152331a9dc