Discussion: #5840

Docs: https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/EventOverview/TextDefaultsBindings/TextDefaultsBindings.html

Reproduction

1. Put the contents below in ~/Library/KeyBindings/DefaultKeyBinding.dict and restart any running programs you want to use it with.
2. Type "HI!"
3. It should get replaced with the emoji but we see intermediate characters as well.

{
  "H" = {
    "I" = {
      "!" = ("insertText:", "👋");
    };
  };
}