Start work on porting unicode input kitten to Go

tools/tui/ui_kitten.go

@@ -0,0 +1,37 @@
+// License: GPLv3 Copyright: 2023, Kovid Goyal, <kovid at kovidgoyal.net>
+
+package tui
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+
+	"kitty/tools/utils"
+)
+
+var _ = fmt.Print
+
+func KittenOutputSerializer() func(any) (string, error) {
+	write_with_escape_code := os.Getenv("KITTEN_RUNNING_AS_UI") != ""
+	os.Unsetenv("KITTEN_RUNNING_AS_UI")
+	if write_with_escape_code {
+		return func(what any) (string, error) {
+			data, err := json.Marshal(what)
+			if err != nil {
+				return "", err
+			}
+			return "\x1bP@kitty-kitten-result|" + utils.UnsafeBytesToString(data) + "\x1b\\", nil
+		}
+	}
+	return func(what any) (string, error) {
+		if sval, ok := what.(string); ok {
+			return sval, nil
+		}
+		data, err := json.MarshalIndent(what, "", "  ")
+		if err != nil {
+			return "", err
+		}
+		return utils.UnsafeBytesToString(data), nil
+	}
+}