[lworld] RFR: 8350961: [lworld] Some VarHandles tests fail when field flattening is not applied [v2]

[Chen Liang]

> #1340 removed null masking for references incorrectly before strict field checks are in place. As a result, we have to mask nulls to default values before the default value concept is gone.

Chen Liang 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 three additional commits since the last revision:

 - Remove problemlist
 - Merge branch 'lworld' of https://github.com/openjdk/valhalla into fix/vh-null-default-mask
 - 8350961: [lworld] Some VarHandles tests fail when field flattening is not applied

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Changes:
  - all: https://git.openjdk.org/valhalla/pull/1385/files
  - new: https://git.openjdk.org/valhalla/pull/1385/files/ed83ae4e..d7deb87e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1385&range=01
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1385&range=00-01

  Stats: 7 lines in 2 files changed: 5 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/valhalla/pull/1385.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1385/head:pull/1385

PR: https://git.openjdk.org/valhalla/pull/1385