HtmlEmbed UI doesn't reflect isEnabled/isReadOnly state

[PhiR42]

📝 Provide detailed reproduction steps (if any)

1. insert a HtmlEmbed block in the editor, type something and save
2. switch the editor to isReadOnly mode
3. It is now impossible to add new HtmlEmbed blocks to the content via the toolbar
4. BUT the "pencil" button to edit existing blocks in the content still works and allows you to modify the html code inside the block.
5. This is a UI bug rather that a functionnality bug since the "save" button on the htmlembed block is disabled, so it is indeed impossible to actually modify the content of the editor.

✔️ Expected result

The "pencil" button of the existing htmlembed blocks in the content should be in disabled state.

❌ Actual result

The "pencil" button of the existing htmlembed blocks is enabled and allows one to change the html code in the block (but not to save it)

[Reinmar]

We discussed this issue internally. Some (random) notes:

• I want to prioritize it because command state is important for some features (comments only mode, e.g).
• Assumption: It goes through commands. Is that correct?
• It may not be a bug... people should perhaps have access to the source of the embed.
• In this case, we should replace the icon, label and... well, review the UI. Big changes needed.
• The source editing is disabled in read-only, though. In CKEditor 4 it is enabled but the source is read-only.
• Plot twist: Link's data is not accessible. Hence, HTML embed's data may not be accessible too. Let's just disable the "Edit button" button (there's no command for that).
• Same line as https://github.com/ckeditor/ckeditor5/blob/1fc2435/packages/ckeditor5-html-embed/src/htmlembedediting.js#L388-L389?

[dawidurbanski]

Fixed in #10570

[oleq]

FYI: I prepared a PR with a ButtonView solution on top of a single unified HtmlEmbedCommand. Ready for review in #10682.

[Reinmar]

Idea: Merge InsertHtmlEmbedCommand and UpdateHtmlEmbedCommand into one command, just like we have in the media embed feature. This will resolve the problem with the latter command (UpdateHtmlEmbedCommand) being disabled and thus disabling buttons.

But, this will mean that when the selection is e.g. in a table in which HTML embed is disallowed (by the schema) the "Edit" buttons on all widgets will be disabled.

Another idea: Have a separate command for updating a given widget (passed to execute()). It's an interesting option, in line with the broad problem that commands should be executable on passed selection (instead of being executable only on the document selection).

Let's ignore this problem, though, because the topic keeps growing beyond control.

Scope:

• Merge the commands.
• Use live instances of ButtonViews
• Clean up detached instances of ButtonViews (ones used in removed widgets).

[dawidurbanski]

Closed in #10682