8142968: Module System implementation
Summary: Initial integration of JEP 200, JEP 260, JEP 261, and JEP 282
Reviewed-by: jjg, jlahoda, vromero, mcimadamore, bpatel, ksrini, darcy, anazarov, dfuchs
Contributed-by: alan.bateman@oracle.com, alex.buckley@oracle.com, jonathan.gibbons@oracle.com, karen.kinnear@oracle.com, mandy.chung@oracle.com, mark.reinhold@oracle.com, jan.lahoda@oracle.com, vicente.romero@oracle.com, andreas.lundblad@oracle.com, andrey.x.nazarov@oracle.com, chris.hegarty@oracle.com, erik.joelsson@oracle.com, kumar.x.srinivasan@oracle.com, sundararajan.athijegannathan@oracle.com

8129962: Investigate performance improvements in langtools combo tests
Summary: New combo API that runs all combo instances in a shared javac context (whenever possible).
Reviewed-by: jjg, jlahoda, vromero