RFR: 8378793: Add ResolvedFieldEntry is_valid assert [v4]

[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

Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:

  Improve assert message.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/29943/files
  - new: https://git.openjdk.org/jdk/pull/29943/files/1b394bca..37c694c7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29943&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29943&range=02-03

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