[lworld] RFR: 8370880: [lworld] Split ciObjArrayKlass into ciRefArrayKlass and ciFlatArrayKlass [v2]

[Quan Anh Mai]

> Hi,
> 
> This PR splits `ciObjArrayKlass` into `ciRefArrayKlass` and `ciFlatArrayKlass`, aligns the hierarchy with the corresponding types of the VM.
> 
> I also had to fix `GraphKit::cast_to_flat_array`, currently it incorrectly assumes that the cast is to an exact type, splitting into `cast_to_flat_array` and `cast_to_flat_array_exact` seems to make it clearer.
> 
> Please kindly review, thanks a lot.

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

  can only infer klass if exact

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Changes:
  - all: https://git.openjdk.org/valhalla/pull/1739/files
  - new: https://git.openjdk.org/valhalla/pull/1739/files/b401f2ff..be614362

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1739&range=01
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1739&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/valhalla/pull/1739.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1739/head:pull/1739

PR: https://git.openjdk.org/valhalla/pull/1739