Add support for installing XAPK files

[DocMcSnappen]

Checklist

• I made sure that there are no existing issues - open or closed - to which I could contribute my information.
• I made sure that there are no existing discussions - open or closed - to which I could contribute my information.
• I have read the FAQs inside the app (Menu -> About -> FAQs) and my problem isn't listed.
• I have taken the time to fill in all the required details. I understand that the request will be dismissed otherwise.
• This issue contains only one feature request.
• I have read and understood the contribution guidelines.

Feature description

File Manager already supports installing APK files, which is awesome. I would like it to also support installing XAPK files.

Why do you want this feature?

To be able to install apps from (for example) APKPure without needing to use their own browser/installer or another separate app. I already use Fossify File Manager as my file manager/installer and it would be great to not need additional apps.

Additional information

Fossify is awesome! 😃