RFR: 8374372: Move OSX Serviceability Agent to macosx namespace

[Harald Eilertsen]

The Mac OSX implementation of the Serviceability Agent and related code is quite different from what's needed from the BSD implementation. Still we have tried to keep the coexisting in one codebase in the out-of-tree BSD port, as that's where the OSX code has been living.

This sometimes cause problems when updates to the Mac OSX port breaks the BSD implementation.

As we are working on getting the BSD port into a state for future upstreaming to the mainline repo, this patch clears the path by moving the Mac OSX implementation of the Servicability Agent to a more fitting namespace.

This should allow us to proceed with the BSD implementation undisturbed, but also without risking breaking the OSX port.

This work was sponsored by The FreeBSD Foundation

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Commit messages:
 - Move Hotspot Agent debugger for MacOSX

Changes: https://git.openjdk.org/jdk/pull/29003/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29003&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8374372
  Stats: 2364 lines in 28 files changed: 1167 ins; 1114 del; 83 mod
  Patch: https://git.openjdk.org/jdk/pull/29003.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29003/head:pull/29003

PR: https://git.openjdk.org/jdk/pull/29003