Begin supporting string16 across the core library

core/encoding/json/marshal.odin

@@ -353,10 +353,10 @@ marshal_to_writer :: proc(w: io.Writer, v: any, opt: ^Marshal_Options) -> (err:
 			#partial switch info in ti.variant {
 			case runtime.Type_Info_String:
 				switch x in v {
-				case string:
-					return x == ""
-				case cstring:
-					return x == nil || x == ""
+				case string:    return x == ""
+				case cstring:   return x == nil || x == ""
+				case string16:  return x == ""
+				case cstring16: return x == nil || x == ""
 				}
 			case runtime.Type_Info_Any:
 				return v.(any) == nil

core/encoding/json/unmarshal.odin

@@ -570,7 +570,9 @@ unmarshal_object :: proc(p: ^Parser, v: any, end_token: Token_Kind) -> (err: Unm
 			key_ptr: rawptr
 
 			#partial switch tk in t.key.variant {
-				case runtime.Type_Info_String:			
+				case runtime.Type_Info_String:
+					assert(!tk.is_utf16)
+
 					key_ptr = rawptr(&key)
 					key_cstr: cstring
 					if reflect.is_cstring(t.key) {