[jdk21u-dev] RFR: 8317677: Specialize Vtablestubs::entry_for() for VtableBlob

[Goetz Lindenmaier]

I backport this for parity with 21.0.4-oracle.

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Commit messages:
 - Backport 1082c0e767a5060d1969edc5ef16f9974e799960

Changes: https://git.openjdk.org/jdk21u-dev/pull/432/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=432&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317677
  Stats: 15 lines in 3 files changed: 8 ins; 1 del; 6 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/432.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/432/head:pull/432

PR: https://git.openjdk.org/jdk21u-dev/pull/432