RFR: 8302873: ZGC: dump barrier data in C2 Mach nodes

[Roberto Castañeda Lozano]

This changeset adds (debug-only) support for printing ZGC barrier data in a human-readable form as part of the C2 Mach node dumps. This is useful for debugging, IGV visualization (e.g. to create [barrier-specific filters](https://user-images.githubusercontent.com/8792647/216639224-aa288dd8-72cc-43a5-a445-a93d65004dac.png)), and for matching nodes in IR test framework checks (e.g. to write [barrier optimization tests](https://github.com/openjdk/zgc/blob/zgc_generational/test/hotspot/jtreg/compiler/gcbarriers/TestZGCBarrierElision.java)).

#### Testing

- tier1 (x64 and aaarch64; linux, windows, and macosx; release and debug mode)
- tested manually that the expected barrier information is dumped when using ZGC
- tested manually that the dumps remain unchanged when using another GC

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Commit messages:
 - Dump barrier data

Changes: https://git.openjdk.org/jdk/pull/12662/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12662&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8302873
  Stats: 38 lines in 4 files changed: 35 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/12662.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12662/head:pull/12662

PR: https://git.openjdk.org/jdk/pull/12662