Add libs/python3.lib to libpython target for SABI builds on Windows

When targeting the Python Stable ABI on Windows (by setting the
Py_LIMITED_API macro to a Python minimum version hex), the unversioned
python3.lib needs to be linked instead of the versioned one
(e.g. python38.lib for Python 3.8).

Python's own config sets the library to link by default in a header
called pyconfig.h (https://github.com/python/cpython/blob/9cc9e277254023c0ca08e1a9e379fd89475ca9c2/PC/pyconfig.h#L270),
which prompts the linker to search for python3.lib if a stable ABI
extension is built using `@rules_python` toolchains.

Since this library is not exported on Windows in the `python_repository()`
rule, it's added now to allow Python SABI extensions to be built (and
linked) on Windows with `@rules_python`.

Since Python takes responsibility for linking the correct lib on Windows,
and never both at the same time, no other changes are made.

python/repositories.bzl

@@ -319,7 +319,7 @@ cc_library(
     name = "libpython",
     hdrs = [":includes"],
     srcs = select({{
-        "@platforms//os:windows": ["python3.dll", "libs/python{python_version_nodot}.lib"],
+        "@platforms//os:windows": ["python3.dll", "libs/python3.lib", "libs/python{python_version_nodot}.lib"],
         "@platforms//os:macos": ["lib/libpython{python_version}.dylib"],
         "@platforms//os:linux": ["lib/libpython{python_version}.so", "lib/libpython{python_version}.so.1.0"],
     }}),