Include use site of deprecated identifiers in deprecation warnings

Currently a deprecation warning reports the line of the import statement that brings the deprecated identifier into scope. I think it would be useful to print the line where the identifier is used, instead.

Steps to reproduce:

module Foo where
import Bar
foo = bar

module Bar where
bar = 23
{-# DEPRECATED bar "use baz instead" #-}

Expected result:

Foo.hs:3:1:
    Warning: In the use of `bar'
             (imported from Bar):
             Deprecated: "use baz instead"

Actual result:

Foo.hs:2:1:
    Warning: In the use of `bar'
             (imported from Bar):
             Deprecated: "use baz instead"

Trac metadata

Trac field	Value
Version	7.4.1
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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