Rewrite taskflow-mapping argument validation

[uranusjr]

This new check now takes account of ti context variables and block
mapping/assigning to them. A few tests are added to validate the
behavior.

---

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In case of fundamental code change, Airflow Improvement Proposal (AIP) is needed.
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[github-actions]

The PR most likely needs to run full matrix of tests because it modifies parts of the core of Airflow. However, committers might decide to merge it quickly and take the risk. If they don't merge it quickly - please rebase it to the latest main at your convenience, or amend the last commit of the PR, and push it with --force-with-lease.

[uranusjr]

Hmm, this is failing with a seemingly unrelated error:

_________________ TestTriggererCommand.test_capacity_argument __________________
  
  self = <tests.cli.commands.test_triggerer_command.TestTriggererCommand testMethod=test_capacity_argument>
  mock_scheduler_job = <MagicMock name='TriggererJob' id='140183951380688'>
  
      @pytest.mark.skipif(not PY37, reason="triggerer subcommand only works with Python 3.7+")
      @mock.patch("airflow.cli.commands.triggerer_command.TriggererJob")
      def test_capacity_argument(
          self,
          mock_scheduler_job,
      ):
          """Ensure that the capacity argument is passed correctly"""
          args = self.parser.parse_args(['triggerer', '--capacity=42'])
          triggerer_command.triggerer(args)
  >       mock_scheduler_job.assert_called_once_with(capacity="42")
  
  tests/cli/commands/test_triggerer_command.py:46: 
  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
  /usr/local/lib/python3.7/unittest/mock.py:889: in assert_called_once_with
      return self.assert_called_with(*args, **kwargs)
  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
  
  _mock_self = <MagicMock name='TriggererJob' id='140183951380688'>, args = ()
  kwargs = {'capacity': '42'}, expected = ((), {'capacity': '42'})
  _error_message = <function NonCallableMock.assert_called_with.<locals>._error_message at 0x7f7f1dceb050>
  actual = call(capacity=42), cause = None
  
      def assert_called_with(_mock_self, *args, **kwargs):
          """assert that the mock was called with the specified arguments.
      
          Raises an AssertionError if the args and keyword args passed in are
          different to the last call to the mock."""
          self = _mock_self
          if self.call_args is None:
              expected = self._format_mock_call_signature(args, kwargs)
              raise AssertionError('Expected call: %s\nNot called' % (expected,))
      
          def _error_message():
              msg = self._format_mock_failure_message(args, kwargs)
              return msg
          expected = self._call_matcher((args, kwargs))
          actual = self._call_matcher(self.call_args)
          if expected != actual:
              cause = expected if isinstance(expected, Exception) else None
  >           raise AssertionError(_error_message()) from cause
  E           AssertionError: Expected call: TriggererJob(capacity='42')
  E           Actual call: TriggererJob(capacity=42)
  
  /usr/local/lib/python3.7/unittest/mock.py:878: AssertionError

Investigating.

[uranusjr]

Looks like #21753 is the cause. Fixing that first. Actually, seems to pass on main? Rebasing.

[uranusjr]

Provider-building job failed without logs. Hopefully unrelated; can’t see how it could be.