AIP-72: Add support for get_current_context in Task SDK

[kaxil]

closes #45234

I am putting the logic for set_current_context in execution_time/context.py. I didn't want to put _CURRENT_CONTEXT in task_sdk/src/airflow/sdk/definitions/contextmanager.py to avoid execution logic in a user-facing module but I couldn't think of another way to store it from execution & allow retrieving (via get_current_context in the Standard Provider) in their Task.

Upcoming PRs:

• Move most of the internal stuff in Task SDK to a separate module.
• Use create_runtime_ti fixture more widely in tests

---

Tested with the following DAG:

import pendulum

from airflow.decorators import dag, task
from airflow.providers.standard.operators.python import get_current_context

@dag(
    schedule=None,
    start_date=pendulum.datetime(2021, 1, 1, tz="UTC"),
    catchup=False,
)
def x_get_context():
    @task
    def template_test(data_interval_end):
        context = get_current_context()

        # Will print `2024-10-10 00:00:00+00:00`.
        # Note how we didn't pass this value when calling the task. Instead
        # it was passed by the decorator from the context
        print(f"data_interval_end: {data_interval_end}")

        # Will print the full context dict
        print(f"context: {context}")

    template_test()

x_get_context()

---

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[amoghrajesh]

Amazing!