[PyROOT] Merge `libROOTPythonizations` and `libJupyROOT`

[guitargeek]

Having only one CPython extension for PyROOT definitely makes things easier. The libJupyROOT was very small.

[github-actions[bot]]

Test Results

     9 files       9 suites   1d 15h 44m 25s :stopwatch:  2 631 tests  2 631 :white_check_mark: 0 :zzz: 0 :x: 22 303 runs  22 303 :white_check_mark: 0 :zzz: 0 :x:

Results for commit fe89d27d.

:recycle: This comment has been updated with latest results.

[pcanal]

What are the changes from a user point of view?

[guitargeek]

There is no change for the user, but for packaging it makes things easier. See also https://github.com/root-project/root/pull/15402.

Actually this is still a draft PR,I first wanted to see if all platforms are happy with the C++ changes. The next step is to move the JupyROOT submodule to ROOT.JupyROOT.

Also this will have no effect on the user, because the user never imports this module themselves: it is implicitly imported by ROOT in a notebook environment.

The overall goal of these PRs is to have a single python module (ROOT) instead of the current 4 (ROOT, JsMVA, JupyROOT, and DistRDF). For packagers, and for Root as a Python package in general, that would make things clearer and easier: from installing root, you get the module ROOT.

[guitargeek]

Rebased on top of master. Failure on macos14 is because of the known xml2 issue.