Integrated: 8310678: [lw5] add implicit constructors

[Vicente Romero]

add support for implicit constructors, add the ImplicitCreation and NullRestricted class file attributes, and the NonAtomic interface

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Commit messages:
 - 8310678: [lw5] add implicit constructors

Changes: https://git.openjdk.org/valhalla/pull/869/files
 Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=869&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8310678
  Stats: 433 lines in 24 files changed: 415 ins; 2 del; 16 mod
  Patch: https://git.openjdk.org/valhalla/pull/869.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/869/head:pull/869

PR: https://git.openjdk.org/valhalla/pull/869