Add scripts for laying ROCM artifacts out for Python packaging.

[stellaraccident]

Functional changes:

• Adds a script linux_python_dist_split.py which materializes build artifacts into a package structure that is conducive for distribute as pip sdists and wheels (additional work will be done to actually overlay the Python packaging artifacts with this for a combined whole).
• Substantial documentation on the packaging design is in that script.
• Adds _therock_utils.artifacts which can be used for introspecting a directory full of build artifacts.
• Adds _therock_utils.exe_stub_gen which can dynamically generate Linux executables which operate as if they were a symlink (since we can't reliably have executable symlinks in Python packages).
• Adds TARGET_NEUTRAL to the SuiteSparse build.

Organizational changes:

• Extracts some Python utilities into an actual package (_therock_utils).
• Moves scripts that were in packaging/portable-linux to the root build_tools and names things consistently (i.e. prefix with linux_).
• Moves portable linux output to /output-linux-portable and adds it to .gitignore.