Add support of update source strings upload for more formats

### Describe the problem

Currently "Update source strings" is only implemented for PO and is invoking msgmerge, what makes it really bound to this format. Support for additional bilingual formats would be great.

### Solution brainstorm

https://docs.translatehouse.org/projects/translate-toolkit/en/latest/commands/pot2po.html could be used for XLIFF files. The code would probably work for other formats as well, it just needs to be tested.

### Describe alternatives you have considered

_No response_

### Screenshots

_No response_

### Additional context

https://github.com/orgs/WeblateOrg/discussions/16503