User-defined visual text substitutions (Prettify Symbols Mode in vim/emacs/vsc)

[spaceunifyfifty]

Check for existing issues

• Completed

Describe the feature

In VSCode among others there are extensions Prettify (not prettier), Conceal
https://marketplace.visualstudio.com/items?itemName=siegebell.prettify-symbols-mode
https://github.com/coq-community/vsc-conceal

which allow you to render matched text as any symbol you want in the editor.
e.g. In python, you can make lambda render as λ

"conceal.substitutions": [
        {
            "language": "python",
            "substitutions": [
                {
                    "ugly": "lambda",
                    "pretty": "λ",
                }
            ]
        }
]

The user still manually types lambda, but immediately after typing it fully the IDE will render it as the symbol. When you move your caret back to the word, it then reveals back as it's original form.

An extension or built-in mode for this would be nice. I currently don't want to use Zed at all for certain languages, because of the lack of the ability to do this.

If applicable, add mockups / screenshots to help present your vision of the feature

No response