[lworld] RFR: 8321039: [lworld] Substitutability code must recognize new annotations [v4]

[Mandy Chung]

> An initial implementation for substitutability test and partial method handle and var handle support for null-restricted types. JDK-8317767 will provide the full library support for null-restricted types.    
> 
> This patch handles null-restricted field reference declared in a non-flat class.  The default value of that field is lazily set by VM on read access.  `Unsafe::getReference` may return null for null-restricted non-flat field.  
> 
> A new `jdk.internal.value.ValueClass` is created to provide JVM entry points for value classes until public APIs are defined.     `jdk.internal.misc.newNullRestrictedArray` method is moved as well.

Mandy Chung has updated the pull request incrementally with one additional commit since the last revision:

  Add back Unsafe::uninitializedDefaultValue used by serializatoin

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Changes:
  - all: https://git.openjdk.org/valhalla/pull/960/files
  - new: https://git.openjdk.org/valhalla/pull/960/files/f1287a44..326d3fc9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=960&range=03
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=960&range=02-03

  Stats: 52 lines in 8 files changed: 23 ins; 26 del; 3 mod
  Patch: https://git.openjdk.org/valhalla/pull/960.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/960/head:pull/960

PR: https://git.openjdk.org/valhalla/pull/960