Little rewrite of HID input (#723)

* change hid sharedmem writing to use structures

Ryujinx.HLE/Input/Keyboard/KeyboardHeader.cs

@@ -0,0 +1,13 @@
+using System.Runtime.InteropServices;
+
+namespace Ryujinx.HLE.Input
+{
+    [StructLayout(LayoutKind.Sequential)]
+    public struct KeyboardHeader
+    {
+        public long Timestamp;
+        public long EntryCount;
+        public long CurrentEntryIndex;
+        public long MaxEntries;
+    }
+}