[BUG] Unable to add application manifests where the binary path is in /usr

[ImSapphire]

Describe the bug
SteamVR runs under pressure-vessel which restricts access to some system paths such as /bin and /usr, and makes them available inside /run/host instead (see the Steam Runtime documentation on shared paths). This results in OpenVR applications where the binary is installed in paths like /usr being ignored by SteamVR when calling IVRApplications::AddApplicationManifest.

To Reproduce
Steps to reproduce the behavior:

1. Install an app (such as WayVR) in a directory which is mounted elsewhere inside pressure-vessel, like /usr
2. Run it
3. When the application calls AddApplicationManifest, the application does not appear inside SteamVR Settings -> Startup / Shutdown, and the following is logged in vrserver.txt:

[Info] - Adding application manifest path: /home/sapphire/.config/wayvr/wayvr.vrmanifest
[Info] - /home/sapphire/.config/wayvr/wayvr.vrmanifest - App wlx-team.wayvr binary_path /usr/bin/wayvr is invalid. Skipping

Expected behavior
The application is registered successfully and can be auto-started by SteamVR.

System Information (please complete the following information):
Please use the latest Steam beta client and SteamVR beta for your bug reports!

• Steam client version (build number or date): 1778003620
• SteamVR version: 2.16.4
• Distribution (e.g. Ubuntu): Arch Linux
• Steam runtime diagnostics: steam-runtime-diagnostics.txt
• Steam and SteamVR logs: logs.tar.gz

Additional context
A possible quick fix could be prepending /run/host/ to the binary path if it's invalid as-is.