Improve "Execute Save Actions on multiple files"

[AB-xdev]

Checklist

• I made sure that there are no existing issues - open or closed - which I could contribute my information to.
• I have taken the time to fill in all the required details. I understand that the feature request will be dismissed otherwise.
• This issue contains only one feature request/enhancement.

Description

There are multiple UX problems with "Execute Save Actions on multiple files":

• The UI freezes during processing
• There is 0 feedback what is done and it also can't be cancelled
• Errors are not reported

Additional information

Related: #129

[AB-xdev]

Partially fixed with version 1.3.0:

Behavior without "Process files asynchronously":

SaveActionsExecOnMultipleFilesUI.webm

Behavior with "Process files asynchronously":

SaveActionsExecOnMultipleFilesUIAsync.webm