The error feedback from the read-string function would be improved if it used an indexing reader.

The read-string function would provide better error feedback if it used an indexing pushback reader
instead of just a plain push back reader. I've seen a number applications that use read-string
to turn long, multiline strings into EDN data, where the additional line number information would be useful.

(Breaking this one off from https://dev.clojure.org/jira/browse/TRDR-44)