Unicode brackets should be opening/closing tokens

Summary

The characters ⟦, ⟧, ⦇, and ⦈ are not recognized as opening/closing tokens as described in proposal #229, causing some expressions to parse with normal brackets but fail with the Unicode variants (or vise versa).

Steps to reproduce

The following GHCi session demonstrates this:

λ> :set -XArrows -XTemplateHaskell -XUnicodeSyntax
λ> f (_, (x, _)) = x
λ> $[|5|]
5
λ> $⟦5⟧

<interactive>:4:1: error: parse error on input ‘$’
λ> (proc x -> (|f|)$[|x|]) 5

<interactive>:5:18: error: Parse error in command: [| x |]
λ> (proc x -> ⦇f⦈$[|x|]) 5
5

Expected behavior

Replacing brackets with their Unicode variants should not affect parsing (as long as -XUnicodeSyntax is enabled). Specifically, in the example above $⟦5⟧ should parse successfully and (proc x -> ⦇f⦈$[|x|]) 5 should result in a parse error.

Environment

• GHC version used: HEAD