[lworld] RFR: 8378256: [lworld] Add guarantees to verify reg_map.location

[Tobias Hartmann]

Similar to code in `frame::saved_oop_result`, we should add guarantees to new Valhalla specific uses of `reg_map.location`.

Thanks,
Tobias

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Commit messages:
 - 8378256: [lworld] Add guarantees to verify reg_map.location

Changes: https://git.openjdk.org/valhalla/pull/2141/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=2141&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8378256
  Stats: 11 lines in 2 files changed: 5 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/valhalla/pull/2141.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/2141/head:pull/2141

PR: https://git.openjdk.org/valhalla/pull/2141