[GHC] #11743: Add unicode support for special brackets (`{| |}` and `[| |]`)

[GHC]

#11743: Add unicode support for special brackets (`{| |}` and `[| |]`)
-------------------------------------+-------------------------------------
           Reporter:  JoshPrice247   |             Owner:  JoshPrice247
               Type:  feature        |            Status:  new
  request                            |
           Priority:  low            |         Milestone:
          Component:  Compiler       |           Version:  7.10.3
  (Parser)                           |
           Keywords:  unicode,       |  Operating System:  Unknown/Multiple
  UnicodeSyntax                      |
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:  2878, 10162
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 This has been mentioned before but didn't have it's own ticket.

 The following where mentioned in #2978, but the respective patch did not
 include them:

  * For TemplateHaskell: `⟦ ⟧` (MATHEMATICAL _ WHITE SQUARE BRACKET) can be
 used instead of `[| |]`
  * For Generics: `⦃ ⦄` (_ WHITE CURLY BRACKET) can be used instead of `{|
 |}`
  * For Arrows: `⦇ ⦈` (Z NOTATION _ IMAGE BRACKET) can be used instead of
 `(| |)`

 Banana brackets were then suggested in #10162 and implemented in
 Phab:D2012 (which has been accepted, but has not yet landed).

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11743>
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