RFR: 8318959: C2: define MachNode::fill_new_machnode() statically

[Roberto Castañeda Lozano]

This changeset makes the implementation of `MachNode::fill_new_machnode()` static instead of ADLC-generated, for better maintainability. The original motivation to generate this function was to replace its logic with a `ShouldNotCallThis()` call for targets that do not define CISC spill or short branch instruction versions. However, most targets (including x64 and aarch64) feature at least one of these and hence do not make use of the ADLC specialization. For those that do, the savings (approximately 140 bytes on a x64 build of `libjvm.so`) are marginal and (arguably) not worth the additional code complexity.

See motivating discussion in https://mail.openjdk.org/pipermail/hotspot-compiler-dev/2023-October/thread.html#69348.

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

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Commit messages:
 - Move definition of fill_new_machnode() to machnode.cpp

Changes: https://git.openjdk.org/jdk/pull/16444/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16444&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8318959
  Stats: 65 lines in 3 files changed: 21 ins; 41 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/16444.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16444/head:pull/16444

PR: https://git.openjdk.org/jdk/pull/16444