[FEATURE REQUEST] Preserve file extension when creating new files (Document Scanner, App Provider etc)

[michaelstingl]

Is your feature request related to a problem? Please describe.
We received user feedback, that users changed the file extension when creating new files (Document Scanner, App Provider etc), so they experienced issues later when they tried to work with this files.

Describe the solution you'd like
In cases, where users create new files of a specific file type, the input field should not allow to change or remove the file extension. Advanced users could always change the file extension later with the "Rename" file action.

Describe alternatives you've considered
n.a.

Additional context

➕ > New document	➕ > Scan document

ownCloud release version 12.0.3 build 282 (Tue Aug 29 16:54:13 CEST 2023)
(app: v12.0.3 - milestone/12.0.3@40dfc92f, sdk: v12.0.3 - develop@740b63e)

TASKS

• Research (if needed)
• Create branch feature/feature_name
• Development tasks
  • Implement whatever
  • ...
• Code review and apply changes requested
• Design test plan
• QA
• Merge branch feature/feature_name into master

PR

• App
• Library (if needed)

[michaelstingl]

Describe alternatives you've considered
n.a.

@felix-schwarz proposed a simpler implementation, and only display a warning message that asks for user confirmation.

…and make document scanner filename pre-selected, similar as the "New document" behavior.

[felix-schwarz]

I eventually ended up implementing a re-usable UITextField subclass that can directly enforce a file extension by dropping all changes and selection to the file extension portion: #1298

[jesmrec]

Done. Ready to 12.1