Scoped kind variables are broken
# Summary
This does work:
```haskell
-- f :: [a -> Either a ()]
f = [Left @a :: forall a. a -> Either a ()]
````
This does not:
```haskell
-- type F :: [a -> Either a ()]
type F = '[Left @a :: forall a. a -> Either a ()]
```
An unfortunate asymmetry between terms & types. See a related discussion at https://gitlab.haskell.org/ghc/ghc/wikis/ghc-kinds/kind-inference/tlks
# Steps to reproduce
```
ghci> :set -XScopedTypeVariables -XDataKinds -XPolyKinds -XTypeApplications
ghci> type F = '[Left @a :: forall a. a -> Either a ()]
<interactive>:3:18: error: Not in scope: type variable ‘a’
```
# Expected behavior
No error.
# Environment
* GHC version used: HEAD.
issue