Add ability to pull XCom when passing multiple map_indexes

[insomnes]

This PR adds the ability to pull XCom when passing multiple map_indexes on RuntimeTaskInstance.

• Update description in doc string
• Pull XCom for each value from the product of all task ids and map indexes
• Fix None case for task id
• Expand original tests

closes: #46665

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[insomnes]

I am still not sure if this is the intended implementation or not, but it is limited by the current execution API restriction of 1 XCom result in response. I didn't touch it to not break anything.

Prints from original DAG example:

    @dag.task
    def xcom_pull(**context):
        ti: TaskInstance = context["ti"]

        # [1, 3, None, None, None, None]
        for x in [
            ti.xcom_pull(task_ids=["identity", "foo", "plusfive"], map_indexes=[0, 2]),
        ]:
            print(x)

[insomnes]

If this PR is not in the right direction I am ok with full rework. I just need to understand what was planned for this feature then.

[amoghrajesh]

Hello @insomnes, apologies for the delayed review. Taking a look at it.

[amoghrajesh]

Initial set of comments, WDYT @ashb?

[insomnes]

@amoghrajesh thanks for the review! No worries about the delay!
I appreciate your time and I’m glad I could contribute to Task SDK development.

[insomnes]

Up. Would be nice to know what's next.

[insomnes]

Up. If this PR should wait for something else or other solution should be chosen, than it would be nice to have some update about it.

[kaxil]

At some point later, we should just maybe expand the API endpoint to optionally get results for multiple map indexes, fine for now!

[amoghrajesh]

Thanks for the patience @insomnes, its taken long to get a review here 🗡️

Few nits, preemptively approving once those are handled.

[insomnes]

Thank you @kaxil and @amoghrajesh for the review.

its taken long to get a review here 🗡️

No problem! I just got a bit lost on the best way to work around the current restrictions of the API, because I don't have a full picture.

I've applied the suggestions as is so I resolved the comments for them

[insomnes]

I've resolved two comments, they were properly fixed, I believe. Still left the thread with the API limitations discussion unresolved, because I am unsure if it is appropriate to do it myself in this case. Other threads were simple fixes.

[insomnes]

Rebased on recent changes to task_runner.py.

[amoghrajesh]

@insomnes i have rebased it again, once green, will merge, thanks for your patience

[insomnes]

@insomnes i have rebased it again, once green, will merge, thanks for your patience

Thank you, checks are green now.
No problem. I am happy to help with the airflow development!