Linux - Replace legacy desktop integration with modern XDG-based integration

Replace manual placement of .desktop files with modern XDG-based install process.

Update .desktop file to leverage modern XDG functions (namely, the ability for an application to request to be ran on the system's most powerful GPU, useful for hybrid graphics setups).

Also provides provisions for launching the viewer on the iGPU and associating SLURLs via the desktop file, accessible by right-clicking the desktop shortcut.

indra/newview/linux_tools/refresh_desktop_app_entry.sh

@@ -2,7 +2,7 @@
 
 VIEWERNAME="Alchemy" #Store the viewer's name as a variable, for portability. This should be correctly capitalized.
 
-CHANNELNAME="AgileAkita" #THIS CAN BE BLANK! Store the viewer's channel (i.e. alpha, beta, etc.) as a variable, for portability. This should be correctly capitalized. Release versions should leave this blank, so the DE will show just VIEWERNAME, not VIEWERNAME CHANNELNAME
+CHANNELNAME="{CHANNELNAME=Test}" #THIS CAN BE BLANK! Store the viewer's channel (i.e. alpha, beta, etc.) as a variable, for portability. This should be correctly capitalized. Release versions should leave this blank, so the DE will show just VIEWERNAME, not VIEWERNAME CHANNELNAME
 
 SCRIPTSRC="$(readlink -f "$0" || echo "$0")"
 RUN_PATH="$(dirname "${SCRIPTSRC}" || echo .)"