Undo and redo in TinyMCE are broken after deleting a view

[azaozz]

As the title. To reproduce:

• Add an image or a gallery to a post using the Add Media button.
• Click on it to select it and delete it (with the backspace or delete key).
• Press Crtl+Z or click on the Undo button in the editor.

22407.patch seems to work well (still includes some debug code for testing). It converts all views to their text mode before adding new undo level in TinyMCE and converts them back to dom nodes when doing redo.

In addition it adds another step when deleting a view, so deleting now does:

• Convert the view to it's text.
• Replace the view wrapper node with a temp span containing that text.
• Run any 'delete' callbacks.
• Remove the temp span keeping its content.
• Cancel the undo level up to this point.
• Delete the view's text (this is captured in the undo level).

This introduces quite a bit of overhead on adding new undo levels in TinyMCE (which happens pretty often, like on every new paragraph or on node changes), but seems to work well with contenteditable=false nodes.

Leaving for 3.6 after ​discussing in IRC.

Moving back to 3.5 and grouping with the rest of the views tickets. When we take a crack at views in the future, we'll create and parcel out tickets from there.

In 22567:

Media: Restore 3.4 editor behavior and remove TinyMCE views.

• Reactivates the wpgallery and wpeditimage TinyMCE plugins. Deactivates the wpviews TinyMCE plugin.
• Moves still-relevant logic from mce-views.js to media-upload.js and shortcode.js.
• No longer include wp-includes/js/mce-views.js. This code will not be used in 3.5, and should be considered unstable.
• Currently, this is the real 3.4 experience; as such, editing triggers the old modals. Changing this is the next major step.

When reassessing views, we should look over all of these tickets and anticipate these bugs accordingly.

fixes #21813, #22123, #22155, #22161, #22257, #22266, #22318, #22407, see #21390.