The idea behind requiring the label is a noble one, but we are not
really using it consistently anyway, and it should be easy to retrofit
later, should we need it.
This also changes our handiling of snippet edits on the client side.
`editor.insertSnippet` unfortunately forces indentation, which we
really don't want to have to deal with. So, let's just implement our
manual hacky way of dealing with a simple subset of snippets we
actually use in rust-analyzer