[jdk15u-dev] RFR: 8273359: CI: ciInstanceKlass::get_canonical_holder() doesn't respect instance size

[Yuri Nesterenko]

to fix the regression where it has been introduced.
The patch applies not exactly clean because of some context differences. The relevant tests run OK: the included test doesn't fail on 15u even before the fix:-(

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Commit messages:
 - Backport f7e9f56e235dc50daae0a85c9790d5b04c9c60f0

Changes: https://git.openjdk.java.net/jdk15u-dev/pull/159/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk15u-dev&pr=159&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8273359
  Stats: 65 lines in 4 files changed: 58 ins; 0 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk15u-dev/pull/159.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk15u-dev pull/159/head:pull/159

PR: https://git.openjdk.java.net/jdk15u-dev/pull/159