Integrated: Merge lworld

[Vicente Romero]

Merge lworld

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Commit messages:
 - Merge branch 'lworld' into universal-tvars_merge_lworld_now
 - Merge lworld
 - changing universal lint warning to unchecked warning
 - Merge lworld
 - Build failing in universal tvars
 - bug: no warning shown for parameterized conversions
 - addressing a NPE in the compiler due to empty warnStack
 - some test refactorings
 - type of TypeVar.ref is incorrect and should be fixed
 - clean up to warnings related code
 - ... and 17 more: https://git.openjdk.java.net/valhalla/compare/9b9365df...eef8bdfb

The merge commit only contains trivial merges, so no merge-specific webrevs have been generated.

Changes: https://git.openjdk.java.net/valhalla/pull/683/files
  Stats: 1563 lines in 36 files changed: 1421 ins; 28 del; 114 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/683.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/683/head:pull/683

PR: https://git.openjdk.java.net/valhalla/pull/683