libarrow-python: Rename to python-pyarrow

`libarrow_python.so` is now a part of `pyarrow` Python module and unable
to build / install separately. It is true that `pyarrow` is installable
through `pip` with some trivial workaround, but I would like to package
this in our official repo for backward compatibility.

packages/python-pyarrow/cpp-cmake_modules-FindPython3Alt.cmake.patch

@@ -0,0 +1,28 @@
+--- a/cpp/cmake_modules/FindPython3Alt.cmake
++++ b/cpp/cmake_modules/FindPython3Alt.cmake
+@@ -58,7 +58,7 @@
+                                                                      Development NumPy)
+ else()
+   find_package(Python3 ${Python3Alt_FIND_PACKAGE_OPTIONS}
+-               COMPONENTS Interpreter Development.Module NumPy)
++               COMPONENTS Interpreter Development.Module)
+ endif()
+ 
+ if(NOT Python3_FOUND)
+@@ -70,7 +70,9 @@
+ set(PYTHON_LIBRARIES ${Python3_LIBRARIES})
+ set(PYTHON_OTHER_LIBS)
+ 
++if(FALSE)
+ get_target_property(NUMPY_INCLUDE_DIRS Python3::NumPy INTERFACE_INCLUDE_DIRECTORIES)
++endif(FALSE)
+ 
+ # CMake's python3_add_library() doesn't apply the required extension suffix,
+ # detect it ourselves.
+@@ -94,5 +96,6 @@
+   set_target_properties(${name} PROPERTIES SUFFIX ${_EXT_SUFFIX})
+ endfunction()
+ 
++include(FindPackageHandleStandardArgs)
+ find_package_handle_standard_args(
+   Python3Alt REQUIRED_VARS PYTHON_EXECUTABLE PYTHON_INCLUDE_DIRS NUMPY_INCLUDE_DIRS)