Integrated: Merge lworld

[Vicente Romero]

Merge lworld into bworld

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

Commit messages:
 - Merge branch 'lworld' into bworld_merge_lworld
 - Classfile signature bang support
 - add different flavors to the useSiteNullChecks compiler option
 - Minor cleanup, preview and since
 - add use site null checks for fields
 - Support for null-restricted types in JShell
 - Fixing null restricted types for fields/methods in compact source files.
 - add use site null checks
 - add the NullRestricted annotation to null restricted fields of value classes
 - Disable null-restricted varargs
 - ... and 106 more: https://git.openjdk.org/valhalla/compare/43b6a738...a3783e4a

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

Changes: https://git.openjdk.org/valhalla/pull/1963/files
  Stats: 7461 lines in 118 files changed: 7195 ins; 57 del; 209 mod
  Patch: https://git.openjdk.org/valhalla/pull/1963.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1963/head:pull/1963

PR: https://git.openjdk.org/valhalla/pull/1963