[Python] Use new scikit-build-core force-include to handle License files instead of custom backend

[raulcd]

Describe the enhancement requested

Scikit-build-core has added the ability to force-include a file out of the source tree. We might be able to remove our custom build backend to manage license and notice files.
See:

• feat: add force-include for sdist, wheel, and build targets scikit-build/scikit-build-core#1364

Component(s)

Python

[raulcd]

We still have to maintain the links on python/LICENSE.txt and python/NOTICE.txt, they are still necessary otherwise the project.license-files metadata validation fails:

Processing ./.
  Added file:///build/python to build tracker '/tmp/pip-build-tracker-2wg3y8uc'
  Created temporary directory: /tmp/pip-modern-metadata-v5_unt9g
  Running command Preparing metadata (pyproject.toml)
  WARNING: tool.scikit-build.metadata is deprecated; use the standard top-level [[tool.dynamic-metadata]] instead
    + Exception Group Traceback (most recent call last):
    |   File "/opt/conda/envs/arrow/lib/python3.11/site-packages/pip/_vendor/pyproject_hooks/_in_process/_in_process.py", line 389, in <module>
    |     main()
    |   File "/opt/conda/envs/arrow/lib/python3.11/site-packages/pip/_vendor/pyproject_hooks/_in_process/_in_process.py", line 373, in main
    |     json_out["return_val"] = hook(**hook_input["kwargs"])
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |   File "/opt/conda/envs/arrow/lib/python3.11/site-packages/pip/_vendor/pyproject_hooks/_in_process/_in_process.py", line 175, in prepare_metadata_for_build_wheel
    |     return hook(metadata_directory, config_settings)
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |   File "/opt/conda/envs/arrow/lib/python3.11/site-packages/scikit_build_core/build/__init__.py", line 102, in prepare_metadata_for_build_wheel
    |     return _build_wheel_impl(
    |            ^^^^^^^^^^^^^^^^^^
    |   File "/opt/conda/envs/arrow/lib/python3.11/site-packages/scikit_build_core/build/wheel.py", line 267, in _build_wheel_impl
    |     return _build_wheel_impl_impl(
    |            ^^^^^^^^^^^^^^^^^^^^^^^
    |   File "/opt/conda/envs/arrow/lib/python3.11/site-packages/scikit_build_core/build/wheel.py", line 324, in _build_wheel_impl_impl
    |     metadata = get_standard_metadata(pyproject, settings, build_state=state)
    |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |   File "/opt/conda/envs/arrow/lib/python3.11/site-packages/scikit_build_core/build/metadata.py", line 119, in get_standard_metadata
    |     metadata = StandardMetadata.from_pyproject(
    |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |   File "/opt/conda/envs/arrow/lib/python3.11/site-packages/scikit_build_core/_vendor/pyproject_metadata/__init__.py", line 563, in from_pyproject
    |     error_collector.finalize("Failed to parse pyproject.toml")
    |   File "/opt/conda/envs/arrow/lib/python3.11/site-packages/scikit_build_core/_vendor/pyproject_metadata/errors.py", line 105, in finalize
    |     raise ExceptionGroup(msg, self.errors)
    | ExceptionGroup: Failed to parse pyproject.toml (2 sub-exceptions)
    +-+---------------- 1 ----------------
      | scikit_build_core._vendor.pyproject_metadata.errors.ConfigurationError: Every pattern in "project.license-files" must match at least one file: 'LICENSE.txt' did not match any
      +---------------- 2 ----------------
      | scikit_build_core._vendor.pyproject_metadata.errors.ConfigurationError: Every pattern in "project.license-files" must match at least one file: 'NOTICE.txt' did not match any
      +------------------------------------
  error: subprocess-exited-with-error
  
  × Preparing metadata (pyproject.toml) did not run successfully.
  │ exit code: 1
  ╰─> No available output.
  
  note: This error originates from a subprocess, and is likely not a problem with pip.
  full command: /opt/conda/envs/arrow/bin/python /opt/conda/envs/arrow/lib/python3.11/site-packages/pip/_vendor/pyproject_hooks/_in_process/_in_process.py prepare_metadata_for_build_wheel /tmp/tmppyo15mt4
  cwd: /build/python
  Preparing metadata (pyproject.toml) ... error
error: metadata-generation-failed

× Encountered error while generating package metadata.
╰─> from file:///build/python

[raulcd]

Issue resolved by pull request 50494
#50494