Q&D adaption to bdist_wheel relocation (fixes #326)

docs/devel/changelog_staging.md

@@ -6,6 +6,7 @@
 # Changelog for next release
 - `PdfPage.get_objects()`: Don't register pageobjects as children, because they don't need to be closed by the caller when part of a page. This avoids excessive caching of weakrefs that are not cleaned up with the object they refer to.
 - Fixed another dotted filepath blunder in the `extract-images` CLI. (The `PdfImage.extract()` API is not affected this time.)
+- Adapted setup code to `bdist_wheel` relocation (moved from wheel to setuptools).
 - Fixed installation with reference bindings (`PDFIUM_BINDINGS=reference`) by adding a missing `mkdir` call and actually including them in the sdist. (In older versions, this can be worked around by cloning the repository and creating the missing directory manually before installation.)
 - Fixed sourcebuild on windows by syncing patches with pdfium-binaries.
 - Updated test expectations: due to changes in pdfium, some numbers are now slightly different.

setup.py

@@ -8,7 +8,10 @@
 import sys
 from pathlib import Path
 import setuptools
-from wheel.bdist_wheel import bdist_wheel
+try:
+    from setuptools.command.bdist_wheel import bdist_wheel
+except ImportError:
+    from wheel.bdist_wheel import bdist_wheel
 from setuptools.command.build_py import build_py as build_py_orig
 
 sys.path.insert(0, str(Path(__file__).parent / "setupsrc"))