Move debuglevel info in version string from PRE to OPT

According to the latest status of the evolving JEP-223 spec, the debuglevel information (e.g. "fastdebug") should not be stored in PRE, but in OPT.

In short, this means that the current split of PRE into PRE_BASE and PRE_DEBUGLEVEL needs to revert to a single PRE, but that on the contrary, OPT needs to split into OPT_BASE and OPT_DEBUGLEVEL.

Also note that the parsing of the version string for --with-version-string needs to be updated as well.

jprt.properties sets the OPT string to JPRT-id. This needs to be changed to set --with-version-opt-base instead.

This change might have further implications down the pipe for consumers of the version string, but that needs to be handled as separate issues.