[lworld] RFR: 8317658: [lworld] TemplateTable::withfield() does not correctly load the ResolvedFieldEntry

[David Simms]

Ensure ResolvedFieldEntry is correctly loaded

More testing might well be in order, but we are more than likely to remove `withfield` . To make up for the testing, using `assert(entry->is_valid())` upon passing to the interpreter runtime is useful for avoiding bugs in future changes to the hand-rolled assembler, that can be error prone when holding a lot of registers (e.g. `putfield`).

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Commit messages:
 - 8317658: [lworld] TemplateTable::withfield() does not correctly load the ResolvedFieldEntry

Changes: https://git.openjdk.org/valhalla/pull/936/files
 Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=936&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317658
  Stats: 32 lines in 5 files changed: 20 ins; 11 del; 1 mod
  Patch: https://git.openjdk.org/valhalla/pull/936.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/936/head:pull/936

PR: https://git.openjdk.org/valhalla/pull/936