[Refactoring] Fix local rename missing occurrences in string interpolations

NameMatcher checked if a StringLiteralExpr was a string segment in an
interpolated string by checking if the parent expression was an
InterpolatedStringLiteralExpr. That's only true pre-type-checking, and unlike
global rename, local rename  uses the type-checked AST.

test/SourceKit/Refactoring/semantic-refactoring/local-rename.swift

@@ -1,6 +1,7 @@
 func foo() {
   var aa = 3
   aa = aa + 1
+  _ = "before \(aa) after"
   return 1
 }