add support for Python 3.10 (#6422)

* add support for Python 3.10

pyarrow is not available, so we are skipping tests for it.
And, restricting `hdfs` extras to be not installed in Python3.10.

Pathlib removed `_init` method and `init` parameter, so just working
around that. It's not a big change.

* skip windows on 3.10; update pip/wheel/setuptools during install

pywin32 is not yet available for 3.10 Python, so skipping those for now

* install libgit2 with Python3.10 as pygit2 wheel is not available

* install libgit2

* only run on macOS, libgit2-1.1 not available on ubuntu

setup.py

@@ -71,7 +71,7 @@ install_requires = [
     "zc.lockfile>=1.2.1",
     "flufl.lock>=3.2,<4",
     "win-unicode-console>=0.5; sys_platform == 'win32'",
-    "pywin32>=225; sys_platform == 'win32'",
+    "pywin32>=225; sys_platform == 'win32' and python_version < '3.10'",
     "networkx>=2.5",
     "psutil>=5.8.0",
     "pydot>=1.2.4",
@@ -99,12 +99,10 @@ gs = ["gcsfs==2021.7.0"]
 gdrive = ["pydrive2[fsspec]>=1.9.0"]
 s3 = ["s3fs==2021.7.0", "aiobotocore[boto3]>1.0.1"]
 azure = ["adlfs==2021.7.1", "azure-identity>=1.4.0", "knack"]
-# https://github.com/Legrandin/pycryptodome/issues/465
 oss = ["ossfs==2021.7.5"]
 ssh = ["sshfs>=2021.7.1"]
 
-# Remove the env marker if/when pyarrow is available for Python3.9
-hdfs = ["pyarrow>=2.0.0"]
+hdfs = ["pyarrow>=2.0.0; python_version < '3.10'"]
 webhdfs = ["hdfs==2.5.8"]
 webdav = ["webdav4>=0.9.0"]
 # gssapi should not be included in all_remotes, because it doesn't have wheels