Linux - Added intiial input provider

src/Avalonia/Artemis.UI.Linux/Providers/Input/LinuxRelativeAxis.cs

@@ -0,0 +1,16 @@
+namespace Artemis.UI.Linux.Providers.Input
+{
+    public enum LinuxRelativeAxis
+    {
+        REL_X = 0x00,
+        REL_Y = 0x01,
+        REL_Z = 0x02,
+        REL_RX = 0x03,
+        REL_RY = 0x04,
+        REL_RZ = 0x05,
+        REL_HWHEEL = 0x06,
+        REL_DIAL = 0x07,
+        REL_WHEEL = 0x08,
+        REL_MISC = 0x09,
+    }
+}