Unable to save edits to existing widgets

[tellthemachines]

Describe the bug

In the new Widgets screen, updating the content of legacy text or HTML widgets doesn't enable the "Update" button, so changes can't be saved.

To reproduce
Steps to reproduce the behavior:

1. Go to the legacy Widgets screen.
2. Add a text or a custom HTML widget and save changes.
3. Switch to the new screen and try to edit the content of that widget.
4. Observe "Update" button still disabled.

Expected behavior

Expected to be able to save any edits in the new screen.

Editor version (please complete the following information):
Latest Gutenberg.

[talldan]

Some previous work on a similar issue - #26144

[Azragh]

I can't save anything on the widgets screen. No matter what I do, when I hit save it only says: "An error occured. [object object]" ..

I found out that I can save legacy widgets when I remove "add_theme_support( 'customize-selective-refresh-widgets' )" from functions.php, but adding blocks still doesn't work. Tested with several themes without other plugins than gutenberg enabled.

[talldan]

The preview option for the text block seems inconsistent too. I tried making some changes and the preview didn't seem to update. It could be related to this issue (or not).

[noisysocks]

#30709 fixed this. The problem was that widgets like Text and Custom HTML use jQuery to trigger the change event.