Multi-language files support

### Describe the problem

Weblate is built on the assumption that each language has its file. But there are translation formats that store all the translation in a single file:

* https://github.com/WeblateOrg/weblate/issues/8676
* https://github.com/WeblateOrg/weblate/issues/6741
* https://github.com/WeblateOrg/weblate/issues/2060
* https://github.com/WeblateOrg/weblate/issues/10848
* https://github.com/WeblateOrg/weblate/issues/14480
* https://github.com/WeblateOrg/weblate/issues/14909
* https://github.com/WeblateOrg/weblate/issues/17241

### Describe the solution you would like

Adjust Weblate core to support such formats:

* Allow to omit `*` in the file mask for such formats
* Make committing work safely with single file - the checksum of the file is currently updated on commit, but it might need to update other translations in this case as well.

### Describe alternatives you have considered

_No response_

### Screenshots

_No response_

### Additional context

_No response_