[lworld] RFR: 8357474: [lworld] Consolidate load/store flat inline types [v9]

[Quan Anh Mai]

> Hi,
> 
> This patch consolidates loading and storing of flat inline types. This makes it so that `make_from_flat` and `store_flat` will take a pointer to the target location. `make_from_flat_array` and `store_flat_array` are split out into their own methods which receive an `idx` parameter. This also fixes some issues I theorycrafted:
> 
> - Improper loading/storing of atomic elements in a non-atomic container. This is not supported at the moment but it would be great to prepare for it.
> - `is_naturally_atomic` checks `nof_declared_nonstatic_fields`, which is incorrect if the sole field has multiple fields. I refactored it into `ciInlineKlass`, the decision to do atomic loads/stores is also delegated to the callee, the caller only needs to know whether the operations act as if they are atomic, not whether they are actually executed atomically.
> - `null_free` of an oop can only be trusted if the container itself is null-free. For example this case:
> 
>         value class StringHolder {
>             @NullRestricted
>             String s;
>         }
> 
>         value class StringHolderHolder {
>             // flatten
>             StringHolder v;
>         }
> 
> Then `v.s` cannot be trusted to be non-null because `v` can be null.
> 
> This also allows straightforward implementation of https://bugs.openjdk.org/browse/JDK-8349110.
> 
> Please let me know what you think. Thanks very much.

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 11 additional commits since the last revision:

 - Merge branch 'lworld' into loadstoreflat
 - cast_to_flat_array
 - weird layout
 - typo
 - generalize weird layout
 - fix array of nullable empty type
 - fix array field calculations
 - array
 - convert_from_payload
 - add tests
 - ... and 1 more: https://git.openjdk.org/valhalla/compare/d1759c70...e49bbc8c

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

Changes:
  - all: https://git.openjdk.org/valhalla/pull/1470/files
  - new: https://git.openjdk.org/valhalla/pull/1470/files/f7e3bd31..e49bbc8c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1470&range=08
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1470&range=07-08

  Stats: 239307 lines in 1636 files changed: 55300 ins; 178981 del; 5026 mod
  Patch: https://git.openjdk.org/valhalla/pull/1470.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1470/head:pull/1470

PR: https://git.openjdk.org/valhalla/pull/1470