refactor(meta): do not store upstream actors in merge node

[wenym1]

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What's changed and what's your intention?

Previously we store the upstream actors information of each actor in the upstream_actor_id of NodeBody::Merge of StreamNode of each StreamActor. This is the only difference of StreamNode for each actor in a same fragment. In this PR, we will change to store the upstream actor information in a separate field besides StreamActor.

We define type alias

pub type ActorUpstreams = BTreeMap<FragmentId, HashSet<ActorId>>;
pub type StreamActorWithUpstreams = (StreamActor, ActorUpstreams);

In code of meta node, most appearance of StreamActor will be replaced with StreamActorWithUpstreams, so that the upstreams information can be carried together with usage to original StreamActor. The field upstream_actor_id of MergeNode and StreamActor is marked deprecated in the proto definition, so that we can review all the original on the fields, to ensure the refactor logic is correct.

Checklist

• I have written necessary rustdoc comments.
• I have added necessary unit tests and integration tests.
• I have added test labels as necessary.
• I have added fuzzing tests or opened an issue to track them.
• My PR contains breaking changes.
• My PR changes performance-critical code, so I will run (micro) benchmarks and present the results.
• My PR contains critical fixes that are necessary to be merged into the latest release.

Documentation

• My PR needs documentation updates.

Release note

[gru-agent]

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[wenym1]

• feat(meta): let stream actors in fragment share same stream node #20310
• refactor(meta): do not store upstream actors in merge node #20222 👈 (View in Graphite)
• main

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