TinyMCE Classic Block: fix the edit image modal

[azaozz]

Editing an image in the Classic Block often fails. The cause is similar to other failures when using modals in the Classic Block TinyMCE instance: a reference to a DOM node is lost after opening the modal.

This was reported first in Gutenberg: ​https://github.com/WordPress/gutenberg/issues/11433. Better to track it here as it is a bug in an old custom WP plugin for TinyMCE.

[azaozz]

In 46085.diff:

• Add a data-* attribute to the selected image before opening the Edit Image modal, then use it to select the image node before applying changes.
• Limit the caption wrapper width when editing in the Classic BLock to the editor width. This is passed from the media modal but is wrong in the Block Editor as it comes from the old $content_width global.
• Some minor cleanup.

[azaozz]

In 46085.1.diff: do not change the caption (shortcode) width when editing in the Classic Block instance. Fix the visual regression with CSS.

[iseulde]

Looks good to me.

[azaozz]

In 44695:

TinyMCE Classic Block: fix the Edit Image modal to work as in the Classic Editor.

Fixes #46085.