RFR: 8298377: JfrVframeStream causes deadlocks in ZGC [v4]

[Erik Österlund]

> The JfrVFrameStream is used while generating stack traces for events. One of the events are the ZPage allocation event. This event is sometimes sent when ZGC is relocating. The current implementation of JfrVFrameStream uses WalkContinuation::include, which causes JFR to walk the continuation and perform GC barriers. This is problematic, since ZGC has a requirement that we never perform load barriers while running the relocation code. If we do, we might end up performing other reloctions from the the relocation code, and in some cases that causes dead locks. 
> 
> I propose that JFR doesn't walk the stack during stack watermark processing. This PR implements that change. This PR replaces https://github.com/openjdk/jdk/pull/11586

Erik Österlund has updated the pull request incrementally with one additional commit since the last revision:

  More renaming

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11778/files
  - new: https://git.openjdk.org/jdk/pull/11778/files/674f0d74..901c4277

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11778&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11778&range=02-03

  Stats: 235 lines in 6 files changed: 114 ins; 114 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/11778.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11778/head:pull/11778

PR: https://git.openjdk.org/jdk/pull/11778