Allow testing src directly

[dobromir-hristov]

Description

This PR allows testing the src files directly, instead of the old way, by building the package first.
The main advantages are speed and debugging. In-code breakpoints now should work properly.
Watch mode also works very fast.

The main changes were:

1. Remove the ~vue/test-utils alias, as it was causing more problems than it was solving.
2. Swap inside webpack the dist of both test-utils and server-utils, with their src, only when in dev testing mode.
3. Allow the old tests against the build to be run. This ensures the end user gets a fully working suite.
4. Change both test-utils and server-test-utils exports from a default exported object to a named export. This should not affect usage after building the package, as we are using cjs format in the end. Adjust where necessary.
5. Rename all references to the old aliases.
6. Add an extra script command to allow testing only in dev mode. This should not change in any way the existing flow.

How to run

If you want to run the tests against the source:

yarn test:unit:only:dev

Thanks to Bogdan for helping debug the initial Webpack config.

[lmiller1990]

I'll pull this down and try it out hopefully in the next day or two, but everything looks like it makes sense... awesome job, I'm really excited to use the watcher for the tests.

Just to confirm my suspicion, when the Karma tests run it still runs the "old" way which is to bundle the entire project and load the dist file?

[dobromir-hristov]

Yep. We only run against the src if you run that command :)
I have tested both workflows and all pass + ci also passes.

[lmiller1990]

Great... if it all works the same, sounds good to me. Just left one comment.

[afontcu]

Looks great! Just added a minor nitpick suggestion.

👍