Linux: Wrapper and scripts modernizations

[Quinn-Elara]

Description

• Updated SLURL handler script to prioritise letting any running viewer handle the SLURL before attempting to launch the defined default SLURL handler. Useful for if the user runs multiple different viewers on a single machine for convenience.
• Updated installation scripts to utilise XDG provided tools to ensure compatibility with as many distros as possible.
• Updated installation scripts to allow for multiple channels of the viewer to be installed simultaneously (e.g. Release and Beta)
• Updated installation scripts to ask if user desires this viewer to be set as the default SLURL handler instead of implicitly assuming.
• Updated desktop file to fix GPU selection on hybrid graphics setups.
• Updated desktop file comment to utilise more common spelling of "online" (see https://www.britannica.com/dictionary/eb/qa/Online-or-on-line- )

Related Issues

---

Checklist

Please ensure the following before requesting review:

• I have provided a clear title and detailed description for this pull request.
• If useful, I have included media such as screenshots and video to show off my changes.
• The PR is linked to a relevant issue with sufficient context.
• I have tested the changes locally and verified they work as intended.
• All new and existing tests pass.
• Code follows the project's style guidelines.
• Documentation has been updated if needed.
• Any dependent changes have been merged and published in downstream modules
• I have reviewed the contributing guidelines.

---

Additional Notes

These changes have been live in Alchemy's release viewers for some time now. This PR is to merge them upstream.

Suggest review from @RyeMutt .

[Geenz]

Thanks - I'll check this out when I'm in front of my Linux box again (currently on a work trip).

[github-actions]

Thank you for your submission, we really appreciate it. Like many open-source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution. You can sign the CLA by just posting a Pull Request Comment same as the below format.

---

I have read the CLA Document and I hereby sign the CLA

---

_{You can retrigger this bot by commenting recheck in this Pull Request. Posted by the CLA Assistant Lite bot.}