Avoids allocation if at all possible. Only allocates if the file path is a quoted string
literal. String literals are necessary in some cases, for example if the file path has
spaces in it. These literals can contain escaped characters which are initially seen as
groups of two characters by the parser (e.g. ‘\’ + ‘n’). A newly allocated string is
used to unescape those characters (e.g. “\n” -> ‘\n’).
Note: While this string is typically a file path, this library makes no attempt to
verify the format of that path. That means that this field can potentially be any
string. You should verify it before doing anything that may be security-critical.