Fix MultiInfo parser + serialization bug (#2265)

* Restore parsed MultiInfo structure in firrtl parser

* Change erroneous expected output in InfoSpec test

FileInfo compression sorts the outputted entries alphabetically, but
this test did not reflect that fact

* Fix typo in comment

* Add unit tests for file locator parsing

* Fix syntax issues and typos

* More redundant braces removed

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>