[lworld] RFR: 8287136: [lw4] Javac tolerates abstract value classes that violate constraints for qualifying to be value super classes

[Srikanth Adayapalam]

Also fixes JDK-8281312 and JDK-8287713

-------------

Commit messages:
 - 8287136: [lw4] Javac tolerates abstract value classes that violate constraints for qualifying to be value super classes

Changes: https://git.openjdk.java.net/valhalla/pull/702/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=702&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8287136
  Stats: 444 lines in 21 files changed: 302 ins; 74 del; 68 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/702.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/702/head:pull/702

PR: https://git.openjdk.java.net/valhalla/pull/702