[lworld] RFR: 8326602: [lworld] substitutabillity test does not support cyclic membership properly

[Mandy Chung]

`test/jdk/valhalla/valuetypes/RecursiveValueClass.java` test fails when the primitive value class is migrated to null-restricted value types.  It uncovers a bug in supporting mutual recursive types. The recursive method handle should be created with the base functions of mutual recursive types so that it can call the recursive method handle for another type properly.

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Commit messages:
 - minor cleanup
 - 8326602: [lworld] substitutabillity test does not support cyclic membership properly

Changes: https://git.openjdk.org/valhalla/pull/1018/files
 Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1018&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8326602
  Stats: 1180 lines in 3 files changed: 766 ins; 348 del; 66 mod
  Patch: https://git.openjdk.org/valhalla/pull/1018.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1018/head:pull/1018

PR: https://git.openjdk.org/valhalla/pull/1018