Remove airflow.utils.xcom module and add backcompat shim

[amoghrajesh]

closes: #53065

All of the occurrences have been handled, just added one missing one in devel-common.

Tested for backcompat issues as users could potentially be using the XCOM_RETURN_KEY from older paths.

DAG:

from airflow.providers.standard.operators.python import PythonOperator
from airflow.sdk import DAG
from airflow.providers.standard.operators.bash import BashOperator


def my_func():
    from airflow.models.xcom import XCOM_RETURN_KEY

    print("New path for return key", XCOM_RETURN_KEY)

    from airflow.utils.xcom import XCOM_RETURN_KEY as old_xcom_return_key
    print("Old path for return key", old_xcom_return_key)

dag = DAG(
    'simple_bash',
    schedule=None,
    catchup=False,
    tags=['example'],
)

hello_task = BashOperator(
    task_id='say_hello',
    bash_command='echo "Hello World from Airflow!"',
    dag=dag,
)

hello_task2 = PythonOperator(
    task_id='say_hello_python',
    python_callable=my_func,
    dag=dag,
)

hello_task >> hello_task2

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