Add FreeBSD support

[djberg96]

Add FreeBSD support

I ripped Ubuntu off my laptop and replaced it with FreeBSD. So, I would like to add support for it here. Ultimately my goal is to get Truffleruby + Graalvm going, but hopefully this helps other projects as well.

This PR was created using Codex (ChatGPT 5.5).

Summary

This PR adds first-class FreeBSD platform detection and wires it through the places where mx currently handles Unix-like hosts.

• Recognizes sys.platform.startswith("freebsd") as canonical OS name freebsd
• Exposes mx.is_freebsd() through the same compatibility path as the existing platform helpers
• Treats FreeBSD like other Unix-like hosts for native library prefixes and suffixes
• Uses /usr/local/openjdk as the default FreeBSD system JDK location
• Includes FreeBSD in IntelliJ SDK discovery and native debug-prefix-map handling
• Marks bundled platform resources without FreeBSD archives as optional rather than trying to consume Linux binaries
• Updates the mx launcher to find common versioned Python 3 executables such as python3.11
• Adds a focused regression test for FreeBSD platform detection and library naming
• Bumps mx version to 7.83.2

Testing

Ran on FreeBSD 15.1 amd64:

./mx --version
./mx --java-home /usr/local/openjdk21 version
/usr/local/bin/python3.11 -m py_compile src/mx/_impl/support/system.py src/mx/_impl/legacy.py src/mx/_impl/mx.py src/mx/_impl/mx_ide_intellij.py src/mx/_impl/mx_fetchjdk.py src/mx/_impl/mx_native.py src/mx/mx_version.py tests/os_arch_tests.py
PYTHONPATH=/home/dberger/Dev/mx/src:/home/dberger/Dev/mx /usr/local/bin/python3.11 -c "from tests import os_arch_tests; os_arch_tests.tests(); print('os_arch_tests ok')"
git diff --check

Notes

Some bundled dependencies, such as Ninja and Eclipse, do not currently publish FreeBSD archives in this suite. Those entries are marked optional for FreeBSD so the platform can bootstrap with locally installed tools instead of failing on unavailable packaged binaries.

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[djberg96]

I've put in a request for an OCA. I thought I had an Oracle account from years ago, but maybe they deleted it because it was stale since I hadn't logged into it in years. Anyway, I have a new one. No clue how long it takes to get approval.

[dougxc]

This change looks good. Once your OCA is approved, I'll integrate it.