[lworld] RFR: 8370450: [lworld] Alternate implementation of the substitutability test method [v3]

[Frederic Parain]

> This is an alternate version of the substitutability method.
> To use it, add -Xshare:off -XX:+UseAltSubstitutabilityMethod to the command line of the Valhalla VM in preview mode.

Frederic Parain has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains four commits:

 - Merge remote-tracking branch 'upstream/lworld' into new_acmp
 - Apply changes suggested in review
 - Merge remote-tracking branch 'upstream/lworld' into new_acmp
 - Add alternate version of the substitutability method

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Changes: https://git.openjdk.org/valhalla/pull/1695/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1695&range=02
  Stats: 337 lines in 18 files changed: 332 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/valhalla/pull/1695.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1695/head:pull/1695

PR: https://git.openjdk.org/valhalla/pull/1695