Can't save an HTML embed after pasting a text from the editor

[Mgsy]

📝 Provide detailed reproduction steps (if any)

1. Insert a new HTML embed/edit the existing one.
2. Select some text in the editor.
3. Copy it.
4. Paste it to the HTML embed.
5. Save changes.

✔️ Expected result

Changes are saved.

❌ Actual result

Nothing happens.

📃 Other details

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[pomek]

The same kind of error (missing selection on the widget element).

1. Insert an empty widget.
2. Use widget type around mechanism, insert a paragraph below.
3. Insert a second widget.
4. Click the first textarea.
5. Type whatever.
6. After saving changes, the second container will be modified.

[pkwasnik]

Another similar case:

1. Insert or edit widget (do not save)
2. Click anywhere outside the widget
3. Try to save
4. Nothing happen

EDIT:

and another one, also connected with #8357 

1. Inset HTML embed widged
2. Enter readonly mode
3. edit button should be disabled, but isn't

[psmyrek]

I've created a follow-up #8509 to provide a generic solution for selecting a widget, which has the data-cke-ignore-events attribute.