RFR: 8159220: Preserve position info in module import and export entries

[Hannes Wallnöfer]

Please review JDK-8159220: Preserve position info in module import and export 
entries

http://cr.openjdk.java.net/~hannesw/8159220/

Note that this is labeled noreg-other as tests will be provided with the ES6 
Parser API.

Thanks,
Hannes