Add option to start with mouse locked on standalone version

Author: schellingb

core_options.h

@@ -53,6 +53,7 @@ namespace DBP_Option
 		_interface_slowrate,
 		_interface_systemhotkeys,
 		_interface_middlemouse,
+		_interface_lockmouse,
 		#endif
 		// General
 		forcefps,
@@ -219,6 +220,17 @@ static retro_core_option_v2_definition option_defs[DBP_Option::_OPTIONS_TOTAL] =
 		},
 		"false"
 	},
+	{
+		"interface_lockmouse",
+		"Mouse Lock Default Status", NULL,
+		"Will have the mouse locked at program start if enabled.", NULL,
+		DBP_OptionCat::General,
+		{
+			{ "false", "Off" },
+			{ "true", "On" },
+		},
+		"false"
+	},
 	#endif
 	{
 		"dosbox_pure_force60fps", // legacy name