FreeDesktop `.desktop` file format support

### Describe the problem

Currently, it seems Weblate doesn't support translating `.desktop` file directly. Users may need to extract strings from `.desktop` file to a known supported format firstly to allow translators translate them on Weblate.

The closest we have is [`ini` format support](https://docs.weblate.org/en/latest/formats/ini.html#ini), but it's still different from what `.desktop` file offers.

### Describe the solution you would like

Directly support `.desktop` file format, like what other platforms did (e.g. [Transifex](https://help.transifex.com/en/articles/6220732-freedesktop)).

### Describe alternatives you have considered

If already supported but I somehow didn't find it, please document it on the website.

### Screenshots

N/A

### Additional context

Related spec: https://specifications.freedesktop.org/desktop-entry-spec/latest/localized-keys.html