package/pkg-python: clean conflicting pep517 packages before install

The python installer package isn't able to overwrite files of packges
that already exist, this causes problems when doing a rebuild or
update without a full clean.

To fix this we can use functionality from importlib to identify and
remove any conflicting python package files before installation.

We also need to use internals from python-installer, as we want to use
the same logic as pyinstaller uses internally for getting the scheme so
that we ensure we clean the correct package scheme (we want it to be the
same as the one we're installing)

Fixes:
Traceback (most recent call last):
  File "/home/buildroot/buildroot/support/scripts/pyinstaller.py", line 69, in <module>
    main()
  File "/home/buildroot/buildroot/support/scripts/pyinstaller.py", line 61, in main
    install(
  File "/home/buildroot/buildroot/output/host/lib/python3.10/site-packages/installer/_core.py", line 109, in install
    record = destination.write_file(
  File "/home/buildroot/buildroot/output/host/lib/python3.10/site-packages/installer/destinations.py", line 207, in write_file
    return self.write_to_fs(scheme, path_, stream, is_executable)
  File "/home/buildroot/buildroot/output/host/lib/python3.10/site-packages/installer/destinations.py", line 167, in write_to_fs
    raise FileExistsError(message)
FileExistsError: File already exists: /home/buildroot/buildroot/output/target/usr/lib/python3.10/site-packages/tinycss2/__init__.py

Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Tested-by: Marcus Hoffmann <marcus.hoffmann@othermo.de>
[yann.morin.1998@free.fr:
  - extend commit log about the use of the installer internals (the
    symbols prefixed with '_')
  - check path.files against explicitly None
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

support/scripts/pyinstaller.py

@@ -2,12 +2,34 @@
 
 import argparse
 import glob
+import pathlib
+
+from importlib.machinery import PathFinder
+from importlib.metadata import DistributionFinder
 
 from installer import install
+from installer._core import _process_WHEEL_file
 from installer.destinations import SchemeDictionaryDestination
 from installer.sources import WheelFile
 
 
+def clean(source, destination):
+    scheme = _process_WHEEL_file(source)
+    scheme_path = destination.scheme_dict[scheme]
+    context = DistributionFinder.Context(
+        name=source.distribution,
+        path=[scheme_path],
+    )
+    for path in PathFinder.find_distributions(context=context):
+        # path.files is either an iterable, or None
+        if path.files is None:
+            continue
+        for file in path.files:
+            file_path = pathlib.Path(file.locate())
+            if file_path.exists():
+                file_path.unlink()
+
+
 def main():
     """Entry point for CLI."""
     ap = argparse.ArgumentParser("python pyinstaller.py")
@@ -58,6 +80,7 @@ def main():
     )
 
     with WheelFile.open(glob.glob(args.wheel_file)[0]) as source:
+        clean(source, destination)
         install(
             source=source,
             destination=destination,