[jdk17u] RFR: 8274338: com/sun/jdi/RedefineCrossEvent.java failed "assert(m != __null) failed: NULL mirror"

[Zhengyu Gu]

A clean backport for parity with Oracle 17.0.3. 

RedefineCrossEvent.java test passed with default, ZGC and Shenandoah GC

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Commit messages:
 - Backport 172aed1a2d75756b140cb723133ac5fb67f7745e

Changes: https://git.openjdk.java.net/jdk17u/pull/226/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk17u&pr=226&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274338
  Stats: 6 lines in 2 files changed: 6 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk17u/pull/226.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk17u pull/226/head:pull/226

PR: https://git.openjdk.java.net/jdk17u/pull/226