Merge conflicting wp.editor objects into a single, non-conflicting module

[adamziel]

Description

Solves WordPress/gutenberg#33203
Solves https://core.trac.wordpress.org/ticket/53437
Related to https://core.trac.wordpress.org/ticket/53569

Situation: packages/editor is exposed as window.wp.editor in wp-admin

Problem: there is quite some code expecting to see a different (legacy) object under window.wp.editor

Proposed solution: export all the members of legacy window.wp.editor from this new module to maintain backward compatibility

As @noisysocks noticed in WordPress/gutenberg#33228:

Makes me wonder if a “fix” could be to add code to Core which fires off doing_it_wrong() if you enqueue wp-editor or wp-edit-post in the widgets screen.

This is addressed in #1484

How has this been tested?

1. Activate classic widgets plugins.
2. Insert text widget
3. Add some text to widget.
4. Deactivate classic widgets plugins.
5. Go to widget screen.
6. There is an error message if this PR is not applied.
7. There are no error messages if this PR is applied.

Screenshots

(Credits for the screenshot and the test plan to @spacedmonkey)

Types of changes

Bug fix (non-breaking change which fixes an issue)