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

[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.

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Commit messages:
 - Add alternate version of the substitutability method

Changes: https://git.openjdk.org/valhalla/pull/1695/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1695&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8370450
  Stats: 334 lines in 18 files changed: 329 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