[lworld] RFR: 8376135: [lworld] Add JIT support for NULLABLE_NON_ATOMIC_FLAT layout [v7]

[Quan Anh Mai]

> Hi,
> 
> This PR implements the support of `NULLABLE_NON_ATOMIC_FLAT` layout in the JITs. There is nothing to do in C2. In C1, I need to implement loading/storing nullable value of a non-atomic field.
> 
> The test `TestValueClasses` is failing with `-XX:-TieredCompilation`, which I suspect is due to the substitutability test handling padding bytes incorrectly.
> 
> Please kindly review what there are for now, thanks a lot.

Quan Anh Mai has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains nine additional commits since the last revision:

 - Remove Strict
 - Merge branch 'lworld' into nullablenonstatic
 - Adjust test, add comments and examples
 - add assert
 - remove unused variable
 - no_null_marker
 - rename null_free in InlineTypeNode::initialize_fields to has_null_marker
 - Fix packing/unpacking adapters, fix some miscelaneous issues, address comment
 - Support NULLABLE_NON_ATOMIC in the JITs

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

Changes:
  - all: https://git.openjdk.org/valhalla/pull/1970/files
  - new: https://git.openjdk.org/valhalla/pull/1970/files/33ba962e..6b1723a3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1970&range=06
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1970&range=05-06

  Stats: 2634 lines in 139 files changed: 1730 ins; 431 del; 473 mod
  Patch: https://git.openjdk.org/valhalla/pull/1970.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1970/head:pull/1970

PR: https://git.openjdk.org/valhalla/pull/1970