[lworld] RFR: 8370450: [lworld] Alternate implementation of the substitutability test method [v8]

[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 incrementally with one additional commit since the last revision:

  Field to field map must be final

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Changes:
  - all: https://git.openjdk.org/valhalla/pull/1695/files
  - new: https://git.openjdk.org/valhalla/pull/1695/files/e9e79fe6..52959d00

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1695&range=07
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1695&range=06-07

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 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