graphics: Check LLVMpipe for Linux software render

[mihawk90]

Description

Adds a check for the Mesa llvmpipe software-rendering on Linux. Also adds a potential solution for Flatpak users.

Not sure on the wording, feedback welcome.

Motivation and Context

This comes up fairly regularly in linux-support on Discord. The most common cause is an updated NVIDIA driver kernel module. On native packages this also updates the userland libraries, but this is not the case for Flatpak. Running flatpak update will sync the userland libraries for the Flatpak runtime, after which OBS runs on the GPU again.

Another cause can be virtualised or containerised environments, which are not supported.

How Has This Been Tested?

Grabbed a log from Discord (truncated to the relevant parts) and ran it through the analyzer:

$ ./loganalyzer.py --file llvmpipe.log 
Critical: Software rendering
Warning:  
Info:     No Output Session, Flatpak | Wayland | KDE (KDE), No Scenes/Sources

--------------------------------------
 
Details

Critical:
Software rendering
    OBS is running on a software-emulated graphics pipeline. This is not
    supported as OBS requires access to a physical GPU. Please make sure your
    graphics drivers are up to date.<br><br>If you are using a NVIDIA GPU,
    please reboot your PC and run <code>flatpak update</code> from a terminal. 

Warning: 

Info:
No Output Session
…

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

• I have read the contributing document.
• My code follows the project's style guidelines
• My code is not on the master branch.
• My code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.