CI/RLS: upgrade to libspatialindex-2.0.0

[mwtoews]

Towards #315.

This PR does the following:

• Upgrade libspatialindex from 1.9.3 to 2.0.0
• Remove the unneeded ci/CMakeLists.txt
• Use cmake install, removing the unneeded lib subdirs
• Remove the soversion number and symlinks for the library name (via CMAKE_PLATFORM_NO_VERSIONED_SONAME=ON)
• It turns out the cibuildwheel tests on different python versions (via tox) was misleading, as it was not testing the built-wheel but the local source tree and sidx library build. This is fixed with pytest --import-mode=importlib
• Consequently, the musllinux wheels on PyPI are "broken", as verified with docker run -it --rm alpine:3.18 /bin/sh --login then apk add py3-pip, pip install rtree, python -c "import rtree" to observe error. This is resolved by setting rpath for libspatialindex described next.
• Use CMAKE_INSTALL_RPATH only for macOS. On Linux, $ORIGIN seems to confuse auditwheel and prevents creation of Rtree.libs. It want's LD_LIBRARY_PATH set while repairing the wheel. But the $ORIGIN rpath is still needed for musllinux, so manually add this last step in repair_wheel.py
• Simplify copying directory trees in setup.py with copy_tree

[hobu]

Waiting on you to merge this @mwtoews. Should we fire a release afterward?

[mwtoews]

there one thing that I'm sorting out before merge, as I want to keep the linux lib dir in Rtree.libs, since I see downstream packages rely on this.

[mwtoews]

There is yet another big list of changes on the build-side, updated in the PR description. This is ready to review by anyone, I'll probably merge it in another day after I've had a chance to carefully review the artefacts.

[EwoutH]

This looks like an amazing clean-up!

One thing I noticed, is that in the build CI vcpython27 is installed on Windows:

https://github.com/Toblerity/rtree/blob/d42650ccd78a413ce016a8528a859ed8ab20c1ee/.github/workflows/deploy.yml#L43-L47

Is this still needed, or can it be updated?

[mwtoews]

It looks like vcpython27 was added in 2020 with #174, at the time when MSBuild was used. Perhaps the existing ilammy/msvc-dev-cmd is sufficient, since cl.exe is needed for cmake -G Ninja (in ci/install_libspatialindex.bat).