gh-36267: Change `ipympl`/`pkgconfig`/`widgetsnbextension` to wheel packages, drop build deps
    
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- Cherry-picked from #36129
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### ⌛ Dependencies

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- Depends on #36239 (merged here)
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URL: #36267
Reported by: Matthias Köppe
Reviewer(s): Dima Pasechnik, github-actions[bot]

Author: Release Manager

build/pkgs/ipympl/checksums.ini

@@ -0,0 +1,5 @@
+tarball=ipympl-VERSION-py2.py3-none-any.whl
+sha1=9848409026669d9edd83074730d7e2456ae8a187
+md5=e08ec29d29955174178b7230d41a7ff7
+cksum=490103438
+upstream_url=https://pypi.io/packages/py2.py3/i/ipympl/ipympl-VERSION-py2.py3-none-any.whl

build/pkgs/ipympl/dependencies

@@ -1,6 +1,4 @@
- ipywidgets matplotlib ipykernel | $(PYTHON_TOOLCHAIN)  jupyter_packaging $(PYTHON)
+ipython numpy ipython_genutils pillow traitlets ipywidgets matplotlib | $(PYTHON_TOOLCHAIN) $(PYTHON)
 
 ----------
 All lines of this file are ignored except the first.
-
-jupyterlab is listed as a "build-system requires", but the package installs correctly without it.

build/pkgs/ipympl/package-version.txt

@@ -0,0 +1 @@
+0.9.3