[GHC] #9796: Implement amap/coerce rule for `Array`

[GHC]

#9796: Implement amap/coerce rule for `Array`
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       Reporter:  dfeuer             |                   Owner:  dfeuer
           Type:  task               |                  Status:  new
       Priority:  normal             |               Milestone:  7.10.1
      Component:  Core Libraries     |                 Version:  7.9
       Keywords:                     |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Easy (less than 1  |         Type of failure:  Runtime
  hour)                              |  performance bug
     Blocked By:                     |               Test Case:
Related Tickets:                     |                Blocking:
                                     |  Differential Revisions:
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 We have `map/coerce`; there's no reason not to have `amap/coerce` as well.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9796>
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