[lworld] RFR: 8372113: [lworld] Fix various issues with TypeAryPtr and TypeAryKlassPtr [v6]

[Quan Anh Mai]

> Hi,
> 
> This PR fixes various issues with `TypeAryPtr` and `TypeAryKlassPtr`. It starts with me trying to tighten the properties (`flat`, `null_free`, etc) of these classes, then fixing all the revealed issues until there are no crashes or wrong results left.
> 
> Please take a look and leave your reviews, thanks a lot.

Quan Anh Mai has updated the pull request incrementally with one additional commit since the last revision:

  Should not clone MergeMem

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Changes:
  - all: https://git.openjdk.org/valhalla/pull/1755/files
  - new: https://git.openjdk.org/valhalla/pull/1755/files/4e927135..2df30c7c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1755&range=05
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1755&range=04-05

  Stats: 8 lines in 1 file changed: 4 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/valhalla/pull/1755.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1755/head:pull/1755

PR: https://git.openjdk.org/valhalla/pull/1755