[lworld] RFR: 8358093: [lworld] Crash when passing invalid constant pool index to early_larval frame

[Matias Saavedra Silva]

An early_larval frame contains a set of constant pool indices that are meant to refer to NameAndTypes. These NameAndType entries should refer to strict fields which must be marked as unset and there exists a verify error and associated test to check this, but there are no checks to ensure the input values actually refer to a NameAndType or valid constant pool index. This patch introduces a new error case and adds a test case to `StrictInstanceFieldsTest`. Note that `StrictInstanceFieldsTest.java` is problem listed so the test will not be used until JTREG 7.6 is integrated.

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Commit messages:
 - Fixed comment
 - 8358093: [lworld] Crash when passing invalid constant pool index to early_larval frame

Changes: https://git.openjdk.org/valhalla/pull/1484/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1484&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8358093
  Stats: 26 lines in 3 files changed: 21 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/valhalla/pull/1484.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1484/head:pull/1484

PR: https://git.openjdk.org/valhalla/pull/1484