[ty] Sort keyword completions above everything else
It looks like VS Code does this forcefully. As in, I don't think we can
override it. It also seems like a plausibly good idea. But by us doing
it too, it makes our completion evaluation framework match real world
conditions. (To the extent that "VS Code" and "real world conditions"
are the same. Which... they aren't. But it's close, since VS Code is so
popular.)
