Type aliases are not checked for scope errors at definition site

[plredmond]

Slack thread: https://liquidhaskell.slack.com/archives/C54QAL9RR/p1616392946007000

{-@ type Foo N = {n:Int | n == N} @-}

{-@ type Bar = Foo {n} @-}

In the definition of Bar the expression variable n isn't in scope, but there's no error.