RFR: 8300255: Introduce interface for GC oop verification in the assembler

[Erik Österlund]

In the assembly code, there is some generic oop verification code. Said verification may or may not fit a particular GC. In particular, it has not worked well for ZGC for a while, and there is an if (UseZGC). This enhancement aims at generalizing this code, such that a collector can have its own oop verification policy.

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Commit messages:
 - 8300255: Introduce interface for GC oop verification in the assembler

Changes: https://git.openjdk.org/jdk/pull/12443/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12443&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8300255
  Stats: 183 lines in 18 files changed: 115 ins; 58 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/12443.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12443/head:pull/12443

PR: https://git.openjdk.org/jdk/pull/12443