[GHC] #15335: Export `findImportUsage` from `rename/RnNames.hs` module

[GHC]

#15335: Export `findImportUsage` from `rename/RnNames.hs` module
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           Reporter:  chshersh       |             Owner:  (none)
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:  8.6.1
          Component:  Compiler       |           Version:  8.4.3
           Keywords:                 |  Operating System:  Unknown/Multiple
  imports,refactoring,export         |
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 I'm writing source plugin for analyzing imports in Haskell source code. I
 don't want to duplicate code already written in GHC. So I would like to
 have `findImportUsage` function and `ImportDeclUsage` type aliases
 exported from `RnNames` module:

 *
 [https://github.com/ghc/ghc/blob/ccd8ce405db89142932daea3fdace8814b110798/compiler/rename/RnNames.hs#L1314-L1318
 GitHub: ghc/compilier/rename/RnNames]

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15335>
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