Allow putting SCC annotations on class instance methods

Perhaps there's a way to do this that I don't know about.

Here's a file:

module Test where                                   

class C a where                                     
  foo :: a -> String                                

instance C Int where                                
  -- this would be a parse error: {-# SCC foo #-}   
  foo a = show a                                    

I want to put a cost center on foo. Like mentioned in the comment, doing that in the obvious way is a parse error.

Interestingly -fprof-auto-top puts a cost center on foo.

This came up when debugging #14637.

Trac metadata

Trac field	Value
Version
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Profiling
Test case
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