RFR: 8378793: Add ResolvedFieldEntry is_valid assert

[Coleen Phillimore]

Please review this small change to add an assert for values in ResolvedFieldEntry, which was useful for debugging at one time.
Tested with tier1-3

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Commit messages:
 - Fix stars
 - 8378793: Add ResolvedFieldEntry is_valid assert

Changes: https://git.openjdk.org/jdk/pull/29943/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29943&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8378793
  Stats: 33 lines in 3 files changed: 25 ins; 1 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/29943.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29943/head:pull/29943

PR: https://git.openjdk.org/jdk/pull/29943