Use the official JSON parser (#1151)

This remove Utf8son and JsonPrettyPrinter dependencies.

NOTE: the standard JSON parser doesn't support configurable
indentation, as a result, all the pretty printed JSON are indented with 2
spaces.

Ryujinx.Common/Configuration/Hid/KeyboardHotkeys.cs

@@ -2,6 +2,6 @@
 {
     public struct KeyboardHotkeys
     {
-        public Key ToggleVsync;
+        public Key ToggleVsync { get; set; }
     }
 }