[lworld] RFR: 8354694: [lworld] Refactor AssertUnsetFields to Early Larval Frame

[Matias Saavedra Silva]

This patch adds refactors so the runtime aligns with the new strict field initialization spec (https://cr.openjdk.org/~dlsmith/jep401/jep401-20250409/specs/strict-fields-jvms.html). The stackmap table entry `AssertUnsetFields` is now referred to as `Early_Larval` and it follows a new format where it is a frame that encompasses a base frame.

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Commit messages:
 - Chen comment
 - 8354694: [lworld] Refactor AssertUnsetFields to Early Larval Frame

Changes: https://git.openjdk.org/valhalla/pull/1435/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1435&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8354694
  Stats: 22 lines in 3 files changed: 18 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/valhalla/pull/1435.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1435/head:pull/1435

PR: https://git.openjdk.org/valhalla/pull/1435