Add basic KMSCON support (closes #886)

It's not perfect yet, but at least it works!

Signed-off-by: AnErrupTion <anerruption@disroot.org>

res/config.ini

@@ -316,8 +316,9 @@ service_name = ly
 # Session log file path
 # This will contain stdout and stderr of Wayland sessions
 # By default it's saved in the user's home directory
-# Important: due to technical limitations, X11 and shell sessions aren't supported, which
-# means you won't get any logs from those sessions.
+# Important: due to technical limitations, X11, shell sessions as well as
+# launching session via KMSCON aren't supported, which means you won't get any
+# logs from those sessions.
 # If null, no session log will be created
 session_log = .local/state/ly-session.log
 

res/ly-kmsconvt@.service

@@ -0,0 +1,17 @@
+[Unit]
+Description=TUI display manager using KMSCON
+After=systemd-user-sessions.service plymouth-quit-wait.service
+After=kmsconvt@%i.service
+Conflicts=kmsconvt@%i.service
+
+[Service]
+ExecStart=$PREFIX_DIRECTORY/bin/kmscon --vt=%I --seats=seat0 --login -- $PREFIX_DIRECTORY/bin/ly --use-kmscon-vt
+StandardInput=tty
+UtmpIdentifier=%I
+TTYPath=/dev/%I
+TTYReset=yes
+TTYVHangup=yes
+TTYVTDisallocate=yes
+
+[Install]
+WantedBy=multi-user.target