[clang][transformer] Change `name` range-selector to return `Error` instead of an invalid range. (#164715)
Previously, when the text in selected range was different from the
decl's name, `name` returned an invalid range, which could cause crashes
if `name` was nested in other range selectors that assumed always valid
ranges. With this change, `name` returns an `Error` if it can't get the
range.