Using Visual Studio Code what is the procedure to:

* Remap a built in command's keyboard shortcut. For example, say, Open File (default is `Ctrl`+`O`, it's unlikely that anyone would actually change this, but the same process should probably apply for any built in shortcut).
* Remap an extension command's keyboard shortcut, say the Bookmark extension's toggle-bookmark (default `Ctrl`+`Alt`+`K`)

IN 2015, this involved editing configuration JSON files, but I don't know which one, or how. In 2021 there's a new UI, how do I find it?