environment: Set up environment variables via systemd

We were setting these in fish shell setup during login. Move them
here so that they can be correctly inherited by systemd services.

Without this, the tmux session service does not get the environment
variables which do not get set by the time tmux session service starts.

https://www.freedesktop.org/software/systemd/man/environment.d.html

environment/.config/environment.d/10-xdg.conf

@@ -0,0 +1,10 @@
+XDG_CONFIG_HOME=$HOME/.config
+XDG_CACHE_HOME=$HOME/.cache
+XDG_DATA_HOME=$HOME/.local/share
+XDG_STATE_HOME=$HOME/.local/state
+
+XDG_SESSION_TYPE=tty
+XDG_SESSION_DESKTOP=sway
+XDG_CURRENT_DESKTOP=sway
+
+SSH_AUTH_SOCK=$XDG_RUNTIME_DIR/ssh-agent.socket

environment/.config/environment.d/20-firefox.conf

@@ -0,0 +1,2 @@
+MOZ_ENABLE_WAYLAND=1
+MOZ_DBUS_REMOTE=1

environment/.config/environment.d/30-qt.conf

@@ -0,0 +1,2 @@
+QT_QPA_PLATFORM=wayland
+QT_QPA_PLATFORMTHEME=qt5ct

environment/.config/environment.d/40-misc.conf

@@ -0,0 +1,9 @@
+MANPAGER=nvim +Man!
+EDITOR=nvim
+VISUAL=nvim
+
+GST_DEBUG_NO_COLOR=1
+GST_DEBUG_COLOR_MODE=off
+GST_DEBUG_DUMP_DOT_DIR=/tmp/gst-dot
+
+GHCUP_USE_XDG_DIRS=1

environment/.config/environment.d/envvars.conf

@@ -1,5 +0,0 @@
-XDG_CURRENT_DESKTOP="sway"
-MOZ_ENABLE_WAYLAND=1
-GTK_USE_PORTAL=0
-QT_QPA_PLATFORM=wayland
-QT_QPA_PLATFORMTHEME=qt5ct