add libinput mouse button mapping support

Here I am remapping button 12 to button 2, which allows me to middle
click with the Fn3 key on my Elecom HUGE trackball.

group_vars/all

@@ -209,6 +209,7 @@ himawaripy:
 
 libinput:
     middle_click_scroll: 12
+    button_mapping: "1 2 3 4 5 6 7 8 9 10 11 2"
 
 display_manager: lightdm
 gdm:

roles/x/tasks/main.yml

@@ -33,6 +33,10 @@
   template: src=30-scroll.conf dest=/etc/X11/xorg.conf.d/30-scroll.conf
   when: libinput.middle_click_scroll is defined
 
+- name: Remap mouse buttons
+  template: src=30-button_mapping.conf dest=/etc/X11/xorg.conf.d/30-button_mapping.conf
+  when: libinput.button_mapping is defined
+
 - include: sxhkd.yml
 - include: unclutter.yml
 - include: autorandr.yml

roles/x/templates/30-button_mapping.conf

@@ -0,0 +1,5 @@
+Section "InputClass"
+        Identifier "libinput button mapping"
+        Driver "libinput"
+        Option "ScrollButton" "{{ libinput.button_mapping }}"
+EndSection