[lworld] RFR: 8329205: [lworld] Add jdk.internal.value.CheckedType API [v2]

[Mandy Chung]

> This PR adds `jdk.internal.value.CheckedType` and other internal APIs for null-restricted value type and array support.   Also rename `Unsafe::isFlattenedArray` to `Unsafe::isFlatArray`.

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

  misc clean up

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Changes:
  - all: https://git.openjdk.org/valhalla/pull/1065/files
  - new: https://git.openjdk.org/valhalla/pull/1065/files/90296ee1..b052b2d3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1065&range=01
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1065&range=00-01

  Stats: 17 lines in 2 files changed: 0 ins; 6 del; 11 mod
  Patch: https://git.openjdk.org/valhalla/pull/1065.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1065/head:pull/1065

PR: https://git.openjdk.org/valhalla/pull/1065