Integrated: Merge lworld

[Vicente Romero]

Merge branch 'lworld' into bworld_merge_lworld

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Commit messages:
 - Merge branch 'lworld' into bworld_merge_lworld
 - Merge lworld
 - improvements to lint warning on method overriding
 - Merge lworld
 - [bworld] Emit lint warnings if overriding method does not have same nullability
 - [bworld] Inference failure with bang
 - Fix RichDiagnosticFormatter not to strip metadata when computing where clauses
 - Merge lworld
 - Show null restriction markers in javadoc.
 - [bworld] Fix iterating arg types for null checks
 - ... and 131 more: https://git.openjdk.org/valhalla/compare/7988e0f2...3bc4d066

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

Changes: https://git.openjdk.org/valhalla/pull/2155/files
  Stats: 8180 lines in 121 files changed: 7702 ins; 148 del; 330 mod
  Patch: https://git.openjdk.org/valhalla/pull/2155.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/2155/head:pull/2155

PR: https://git.openjdk.org/valhalla/pull/2155