RFR: 8330262: C2: simplify transfer of GC barrier data from Ideal to Mach nodes

[Roberto Castañeda Lozano]

This (trivial?) cleanup reuses `MemNode::barrier_data()` (added recently by [JDK-8322692](https://bugs.openjdk.org/browse/JDK-8322692)) to compute the GC barrier data to be transferred from Ideal nodes to their corresponding Mach nodes in `Matcher::ReduceInst()`.

**Testing:** tier1-3 (windows-x64, linux-x64, linux-aarch64, and macosx-x64; release and debug mode).

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Commit messages:
 - Simplify transfer of GC barrier data from Ideal to Mach nodes

Changes: https://git.openjdk.org/jdk/pull/18784/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18784&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8330262
  Stats: 5 lines in 1 file changed: 0 ins; 4 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/18784.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18784/head:pull/18784

PR: https://git.openjdk.org/jdk/pull/18784