RFR: Merge lworld [v2]

[Vicente Romero]

> Merge branch 'lworld' into bworld_merge_lworld

Vicente Romero has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 125 commits:

 - Merge branch 'lworld' into bworld_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
 - javac should not place initializers of null restricted fields before the super invocation
   
   Reviewed-by: liach
 - Merge lworld
 - fixing bug in null checks generation
   
   Co-authored-by: Jan Lahoda <jlahoda at openjdk.org>
   Reviewed-by: jlahoda
 - Removing commented tests
 - Merge lworld
 - ... and 115 more: https://git.openjdk.org/valhalla/compare/8b04a6e3...ba674eed

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Changes: https://git.openjdk.org/valhalla/pull/2038/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=2038&range=01
  Stats: 8110 lines in 116 files changed: 7778 ins; 64 del; 268 mod
  Patch: https://git.openjdk.org/valhalla/pull/2038.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/2038/head:pull/2038

PR: https://git.openjdk.org/valhalla/pull/2038