Packages: Extract dom package and make it maintained with Lerna

[gziolo]

Description

Related issues: #3955, #6594.

This PR tries to provide Lerna setup similar to what we have in WordPress/packages. This would allow publishing source code of individual modules to npm to make them available for all plugin developers.

This PR extract new dom package which contains all DOM utils.

Open question

Question is if we should also provide deprecation message for all moved functions from @wordpress/utils?

How has this been tested?

Manually:

• Removed node_modules folder.
• npm install
• npm test
• npm run dev
• npm run build
• npm run package-plugin

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code has proper inline documentation.

[ntwb]

LGTM 👍

[ntwb]

👍

[ntwb]

Possible merge conflict with #6756 when it comes time to merge

[gziolo]

Added deprecation for all dom utils in wp.utils and rebased with master.

[gziolo]

There are packages which depend on react and react-dom and it produces warnings when they are only hoisted, too early to remove them from root file…

The same applies to moment and tinymce, the only difference is that nothing warns :)
Removing c367c49 from this PR.