[Feature Request]: Optimize [multi]map side inputs.

[robertwb]

What would you like to happen?

Currently the only way to read a map is key-by-key lookup. While this works great for too-large-to-fit-into-memory maps, for smaller maps (which are commonly used) this is very inefficient.

Issue Priority

Priority: 2 (default / most feature requests should be filed as P2)

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[jrmccluskey]

@robertwb is work completed on this task?

[robertwb]

The attached PRs should resolve the issue for the SDK and local runners.