Make compatible with Jinja2 3.1+

[roger.oberholtzer@…]

When trying to load this plugin in Trac 1.5 / Python 3 (3.10), the trac log reports:

2022-09-08 15:22:38,544 Trac[loader] ERROR: Skipping "TracXMLRPC = tracrpc":
Traceback (most recent call last):
  File "/usr/lib/python3.10/site-packages/Trac-1.5.4.dev0-py3.10.egg/trac/loader.py", line 80, in _load_eggs
    entry.load(require=True)
  File "/usr/lib/python3.10/site-packages/pkg_resources/__init__.py", line 2471, in load
    return self.resolve()
  File "/usr/lib/python3.10/site-packages/pkg_resources/__init__.py", line 2477, in resolve
    module = __import__(self.module_name, fromlist=['__name__'], level=0)
  File "/usr/lib/python3.10/site-packages/TracXMLRPC-1.2.0.dev0-py3.10.egg/tracrpc/__init__.py", line 16, in <module>
    from tracrpc.web_ui import *
  File "/usr/lib/python3.10/site-packages/TracXMLRPC-1.2.0.dev0-py3.10.egg/tracrpc/web_ui.py", line 45, in <module>
    class RPCWeb(Component):
  File "/usr/lib/python3.10/site-packages/TracXMLRPC-1.2.0.dev0-py3.10.egg/tracrpc/web_ui.py", line 153, in RPCWeb
    _expand_docs_jinja = jinja2.contextfunction(_expand_docs_jinja)
AttributeError: module 'jinja2' has no attribute 'contextfunction'

This with version 18497.

[Jun Omae]

jinja2.contextfunction is replaced by jinja2.pass_context in Jinja2 3.1.0.

See also ​https://jinja.palletsprojects.com/en/3.1.x/changes/#version-3-1-0

[Jun Omae]

Fixed in [18512].