Use python_site_packages_path when specified

[jjhelmus]

I'm putting this up as an example and for discussion. More work is needed for a complete implementation, especially given that this one breaks backwards compatibility in various function.

Description

When the python package in an environment specifies a python_site_packages_path in its repodata entry, use that path to install noarch: python packages.

Note that this currently only works with the classic solver as libmamba/conda-libmamba-solver does not yet understand this field.

Refs #14053.

Checklist - did you ...

• Add a file to the news directory (using the template) for the next release's release notes?
• Add / update necessary tests?
• Add / update outdated documentation?

[jjhelmus]

An example of this:

❯ conda create -n example -c jjhelmus/label/sp_path -c conda-forge python=3.99.90 imagesize --solver classic --yes
Collecting package metadata (current_repodata.json): done
Solving environment: done

## Package Plan ##

  environment location: /Users/jhelmus/workspace/conda/devenv/Darwin/arm64/envs/devenv-3.10-c/envs/example

  added / updated specs:
    - imagesize
    - python=3.99.90


The following NEW packages will be INSTALLED:

  imagesize          conda-forge/noarch::imagesize-1.4.1-pyhd8ed1ab_0 
  python             jjhelmus/label/sp_path/noarch::python-3.99.90-0 



Downloading and Extracting Packages:

Preparing transaction: done
Verifying transaction: done
Executing transaction: done
#
# To activate this environment, use
#
#     $ conda activate example
#
# To deactivate an active environment, use
#
#     $ conda deactivate

❯ tree /Users/jhelmus/workspace/conda/devenv/Darwin/arm64/envs/devenv-3.10-c/envs/example
/Users/jhelmus/workspace/conda/devenv/Darwin/arm64/envs/devenv-3.10-c/envs/example
├── conda-meta
│   ├── history
│   ├── imagesize-1.4.1-pyhd8ed1ab_0.json
│   └── python-3.99.90-0.json
└── sample_path
    └── from_the_file
        └── index_json
            ├── imagesize
            │   ├── __init__.py
            │   └── imagesize.py
            └── imagesize-1.4.1.dist-info
                ├── INSTALLER
                ├── LICENSE.rst
                ├── METADATA
                ├── RECORD
                ├── REQUESTED
                ├── WHEEL
                ├── direct_url.json
                └── top_level.txt

7 directories, 13 files

The python package used here was created with conda-build that includes the change from conda/conda-build#5502.