build: check if libinput supports high-res scroll

Starting with Linux Kernel v5.0 two new axes are available for
mice that support high-resolution wheel scrolling: REL_WHEEL_HI_RES and
REL_HWHEEL_HI_RES.

Both axes send data in fractions of 120 where each multiple of 120
amounts to one logical scroll event. Fractions of 120 indicate a wheel
movement less than one detent.

Three new events are now available on libinput:
LIBINPUT_EVENT_POINTER_SCROLL_WHEEL,
LIBINPUT_EVENT_POINTER_SCROLL_FINGER, and
LIBINPUT_EVENT_POINTER_SCROLL_CONTINUOUS.
These events replace the LIBINPUT_EVENT_POINTER_AXIS event, so new
clients should simply ignore that event.

Also, two new APIs are available to access the high-resolution data:
libinput_event_pointer_get_scroll_value() and
libinput_event_pointer_get_scroll_value_v120().

Add a project argument (LIBINPUT_HAS_SCROLL_VALUE120) to allow
building against old versions of libinput or, where high-resolution
scroll is available, support it.

backend/libinput/meson.build

@@ -28,8 +28,8 @@ wlr_files += files(
 features += { 'libinput-backend': true }
 wlr_deps += libinput
 
-# libinput hold gestures are available since 1.19.0
-add_project_arguments(
+# libinput hold gestures and high resolution scroll are available since 1.19.0
+add_project_arguments([
 	'-DLIBINPUT_HAS_HOLD_GESTURES=@0@'.format(libinput.version().version_compare('>=1.19.0').to_int()),
-	language: 'c',
-)
+	'-DLIBINPUT_HAS_SCROLL_VALUE120=@0@'.format(libinput.version().version_compare('>=1.19.0').to_int()),
+], language: 'c')