[crac] RFR: 8353241: [CRaC] Support ZGC [v4]

[Radim Vansa]

> During my tests with https://github.com/CRaC/example-spring-boot I could not get the image size as low as with G1, but the presented changes improve the image footprint. As as anecdotal data, the image is 177 MB with G1 while 215 MB with ZGC (fastdebug build, `-Xmx1G`).

Radim Vansa has updated the pull request incrementally with one additional commit since the last revision:

  Address review comments

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Changes:
  - all: https://git.openjdk.org/crac/pull/219/files
  - new: https://git.openjdk.org/crac/pull/219/files/75e2bc41..3b7d15e7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=crac&pr=219&range=03
 - incr: https://webrevs.openjdk.org/?repo=crac&pr=219&range=02-03

  Stats: 12 lines in 6 files changed: 0 ins; 7 del; 5 mod
  Patch: https://git.openjdk.org/crac/pull/219.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/219/head:pull/219

PR: https://git.openjdk.org/crac/pull/219