[Problem] UI/UX: Toolbar customization is awkward and default toolbars cannot be modified.

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Problem description

Issue to group related issues of the mentioned problem at the FreeCAD Day 2024 Complaint Session:
**Toolbar customization is awkward and default toolbars cannot be modified**
also
**On small screens the user interface is truncated, the default toolbars do not wrap around.**

Related issues:

- https://github.com/FreeCAD/FreeCAD/issues/9926
- https://github.com/FreeCAD/FreeCAD/issues/11371
- https://github.com/FreeCAD/FreeCAD/issues/11354
- https://github.com/FreeCAD/FreeCAD/issues/6097
- https://github.com/FreeCAD/FreeCAD/issues/10177
- https://github.com/FreeCAD/FreeCAD/issues/8532
- https://github.com/FreeCAD/FreeCAD/issues/7882
- https://github.com/FreeCAD/FreeCAD/issues/6062
- https://github.com/FreeCAD/FreeCAD/issues/11208
- https://github.com/FreeCAD/FreeCAD/issues/10694

### Full version info

```shell
0.22
```

### Subproject(s) affected?

Core

### Anything else?

_No response_

### Code of Conduct

- [X] I agree to follow this project's Code of Conduct

Review the related issues listed in #12697 to understand the separate toolbar customization and small-screen layout problems. The issue is complete only when a specific, agreed scope and behavior for modifying default toolbars and handling truncated toolbars has been defined and implemented.

Written by the indexing model from the issue text.