This converts the instances of the pattern for which we have a proper
substitution in lit. This will make it easier to replace it
appropriately with Windows equivalents.
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.
