RFR: 8313554: Fix -Wconversion warnings for ResolvedFieldEntry

Wed Aug 2 20:19:06 UTC 2023

The recent change in [JDK-8301996](https://bugs.openjdk.org/browse/JDK-8301996) added more -Wconversion warnings that are addressed in this patch. The aforementioned change has overlooked inconsistencies with the types used by `ResolvedFieldEntry` and the method `fill_in()`. Verified with tier 1-4 tests.

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Commit messages:
 - 8313554: Fix -Wconversion warnings for ResolvedFieldEntry

Changes: https://git.openjdk.org/jdk/pull/15126/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15126&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8313554
  Stats: 9 lines in 3 files changed: 2 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/15126.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15126/head:pull/15126

PR: https://git.openjdk.org/jdk/pull/15126