Add support for custom icon emoji in bottom buttons (Mini Apps v9.5)

[wishyoudie]

Added support for custom icons (represented as custom emoji ids) in bottom bar buttons (MainButton, SecondaryButton). Custom icon is a string parameter, set to empty string by default. They were added in Bot API v9.5 on March 1st.

Custom icons can be seen in action in asmico bot. At the time of writing, they are not supported on macOS client (they appear invisible), but at least iOS and webk clients work fine.

Demo was captured in webk and scaffolded from apps/playground with the following code:

import { init, mainButton } from "@/sdk";

init();
mainButton.mount();
mainButton.setParams({
  text: "Hello",
  textColor: "#ffffff",
  bgColor: "#000000",
  iconCustomEmojiId: "5465665476971471368",
  isVisible: true,
});

// mainButton.setIconCustomEmojiId("5465665476971471368"); // also checked with standalone method

[heyqbnk]

Thank you!