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

 #!/bin/bash
 
+# Cannot get this CMake feature to work; fill in manually for now
+#VIEWERNAME="@VIEWER_CHANNEL_BASE@" #This should be the viewer's canonical base name, e.g. Second Life, Firestorm, Alchemy, etc. Handled by cmake.
+
+#CHANNELNAME="@VIEWER_CHANNEL_TYPE@ @VIEWER_PROJECT_CODENAME@" #Use cmake to autofill the channel type (alpha, beta, release), and any project codename.
+VIEWERNAME="Alchemy" #This should be the viewer's canonical base name, e.g. Second Life, Firestorm, Alchemy, etc. Handled by cmake.
+CHANNEL_TYPE=""
+PROJECT_NAME=""
+
+CHANNELNAME="${CHANNEL_TYPE} ${PROJECT_NAME}" #Use cmake to autofill the channel type (alpha, beta, release), and any project codename.
+
+CHANNELNOBREAK=$(echo $CHANNELNAME | tr " " "-") #Store a version of the channel name without any spaces to prevent breakage with some functions. Not filled by cmake to ensure consistency in it's output.
+
 SCRIPTSRC="$(readlink -f "$0" || echo "$0")"
 RUN_PATH="$(dirname "${SCRIPTSRC}" || echo .)"
 
-install_prefix="${RUN_PATH}"/..
+install_prefix=$(builtin cd "${RUN_PATH}/.." || exit; pwd) #This is a cleaner way of getting the absolute path for the install directory.
+
+function print() {
+	log_prefix="${VIEWERNAME} ${CHANNELNAME} Desktop Integration:"
+	echo -e "${log_prefix} $*"
+}
+
 
 function install_desktop_entry()
 {
 	local installation_prefix="${1}"
-	local desktop_entries_dir="${2}"
-
-	local desktop_entry="\
-[Desktop Entry]\n\
-Name=Alchemy\n\
-Comment=Client for the On-line Virtual World, Second Life\n\
-Exec=${installation_prefix}/alchemy\n\
-Icon=${installation_prefix}/alchemy_icon.png\n\
-Terminal=false\n\
-Type=Application\n\
-Categories=Game;Simulation;\n\
-StartupNotify=true\n\
-StartupWMClass=Alchemy\n\
-X-Desktop-File-Install-Version=3.0"
-
-	echo " - Installing menu entries in ${desktop_entries_dir}"
-	mkdir -vp "${desktop_entries_dir}"
-	echo -e "${desktop_entry}" > "${desktop_entries_dir}/alchemy-viewer.desktop" || "Failed to install application menu!"
+
+	desktoppath="${installation_prefix}/${VIEWERNAME,,}-${CHANNELNOBREAK,,}-viewer.desktop"
+	cat >"${desktoppath}" <<desktopfile || print "Warning: Could not write $desktoppath"s
+[Desktop Entry]
+Version=1.4
+Name=${VIEWERNAME} ${CHANNELNAME}
+GenericName=Second Life Viewer
+Comment=Client for the Online Virtual World, Second Life
+Exec=${installation_prefix}/${VIEWERNAME,,}
+Icon=${VIEWERNAME}-${CHANNELNOBREAK}-Viewer
+Terminal=false
+Type=Application
+Categories=Game;Simulation;
+StartupNotify=true
+StartupWMClass=${VIEWERNAME} ${CHANNELNAME}
+PrefersNonDefaultGPU=true
+Actions=DefaultGPU;AssociateMIME;
+
+[Desktop Action DefaultGPU]
+Exec=env __GLX_VENDOR_LIBRARY_NAME="" ${installation_prefix}/${VIEWERNAME,,}
+Name=Launch on default GPU
+
+[Desktop Action AssociateMIME]
+Exec=${installation_prefix}/etc/register_secondlifeprotocol.sh
+Name=Associate SLURLs
+desktopfile
+
+#The above adds some options when the shortcut is right-clicked, to launch on the default (usually integrated) GPU, and to force MIME type association.
+
+#The "PrefersNonDefaultGPU" line should automatically run the viewer on the most powerful GPU in the system, if it is not default. If it is, this is ignored.
+
+# NOTE: DO NOT CHANGE THE "GenericName" FIELD - ONLY CHANGE THE "Name" FIELD. (This is to ensure that searching "Second Life" will show all the viewers installed in a user's system, regardless of their canonical name.)
+
+	print "Installing menu entries via XDG..."
+	xdg-icon-resource install --novendor --size 256 "${install_prefix}/${VIEWERNAME,,}_icon.png" "${VIEWERNAME}"-"${CHANNELNOBREAK}"-Viewer
+	#NOTE: Above command takes the path to the icon to install && The name of the icon to be used by XDG. This should always be in the format of "x-Viewer" to avoid potential naming conflicts, as per XDG spec.
+	xdg-desktop-menu install --novendor "${installation_prefix}"/"${VIEWERNAME,,}"-"${CHANNELNOBREAK,,}"-viewer.desktop
 }
 
+CHANNELNAME=$(echo "${CHANNELNAME}" | xargs) #Trim leading and / or tailing whitespace from CHANNELNAME
 if [ "$UID" == "0" ]; then
 	# system-wide
 	install_desktop_entry "${install_prefix}" /usr/local/share/applications