Currently, if multiple --add-modules options are specified on the Java command line the last one wins and the previous ones are ignored.

Instead of ignoring the previous --add-modules options, have it combine all values so that

   java --add-modules a --add-modules b

would be equivalent to: java --add-modules a,b

In addition, --add-exports and --add-reads options do not accept duplicated module/package and it is an error to attempt to export the same package more than once on the command-line.

Merging multiple --add-exports option with the same module/package appears in several options may not always be feasible (e.g. _JAVA_OPTIONS, _JAVAC_OPTIONS and argfiles etc).

This also proposes to change --add-exports and --add-reads CLI options to allow repeating with the same module/package.