RFR: Merge lworld [v2]

[Chen Liang]

> Merge now to fix conflicts from ACC_STRICT_INIT renames.

Chen Liang has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 130 commits:

 - Merge branch 'lworld' of https://github.com/openjdk/valhalla into bworld-merge-lworld
 - [bworld] fixing regression tests
   
   Reviewed-by: liach
 - [bworld] javac crash for abstract methods with null restricted arguments
   
   Reviewed-by: liach
 - [bworld] BasicAccessFlags and JavaBaseCheckSince failing
 - JVM detect null checked flag
   
   Reviewed-by: vromero
 - Merge lworld
 - Merge lworld
 - Remove redundant null checks
   
   Reviewed-by: mcimadamore
 - add javac and javap support for the ACC_NULL_CHECKED flag
   
   Reviewed-by: liach
 - Merge lworld
 - ... and 120 more: https://git.openjdk.org/valhalla/compare/e7d07ae0...2baf0d95

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Changes: https://git.openjdk.org/valhalla/pull/2052/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=2052&range=01
  Stats: 8196 lines in 130 files changed: 7801 ins; 95 del; 300 mod
  Patch: https://git.openjdk.org/valhalla/pull/2052.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/2052/head:pull/2052

PR: https://git.openjdk.org/valhalla/pull/2052