[FixCode] Apply coercion fixit for assignment types' mismatch too. rdar://27681428

Author: nkcsgexi

lib/Sema/CSDiag.cpp

@@ -4014,6 +4014,7 @@ bool FailureDiagnosis::diagnoseContextualConversionError() {
   case CTP_ArrayElement:
   case CTP_DictionaryKey:
   case CTP_DictionaryValue:
+  case CTP_AssignSource:
     tryRawRepresentableFixIts(diag, CS, exprType, contextualType,
                               KnownProtocolKind::ExpressibleByIntegerLiteral,
                               expr) ||

test/FixCode/fixits-apply.swift

@@ -261,3 +261,12 @@ func disable_unnamed_param_reorder(p: Int, _: String) {}
 disable_unnamed_param_reorder(0, "") // no change.
 
 prefix operator ***** {}
+
+func foo(an : Any) {
+  let a1 : AnyObject
+  a1 = an
+  let a2 : AnyObject?
+  a2 = an
+  let a3 : AnyObject!
+  a3 = an
+}

test/FixCode/fixits-apply.swift.result

@@ -264,3 +264,12 @@ func disable_unnamed_param_reorder(p: Int, _: String) {}
 disable_unnamed_param_reorder(0, "") // no change.
 
 prefix operator *****
+
+func foo(an : Any) {
+  let a1 : AnyObject
+  a1 = an as AnyObject
+  let a2 : AnyObject?
+  a2 = an as AnyObject?
+  let a3 : AnyObject!
+  a3 = an as AnyObject!
+}