Some of the implicit decls generated for lazy vars have invalid source ranges.
For now, just always walk into implicit decls when looking for name locations.
Resolves rdar://problem/35255644.
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.
