This can fix a lot of performance issues, like audio crackling and frame
time spikes. This requires the GameMode package to be installed. See:
https://github.com/FeralInteractive/gamemode
This commit adds a "Game Mode" bool option to the "Power
Management" and "Latency" settings sections, and it can be toggled
on/off without restarting RA.
The actual toggling of game mode happens in a new frontend platform
interface function. Perhaps this will become useful for other platforms
that provide some equivalent of Linux GameMode.
Since the GameMode ABI is fixed, and the API comes as a single,
header-only file with no actual deps, we simply bundle the header
(deps/feralgamemode/gamemode_client.h.) That way, all Linux builds will
have support for GameMode regardless of whether the GameMode development
package is installed or not.
