map_rect with fixed integer and real data across shards

Description

Currently the integer and real data vary by shard in calls to map_rect. In some situations, there is fixed integer or real data per shard. Adding extra arguments for those would allow them to be shared.

This request is transcribed from this forum post by Robert Kubinec, the body of which is:

I have a proposal for what I hope would be a small change to the map_rect function, which I have come to use a lot. Currently the function takes an array of integers, an array of reals, each varying by shard, an array of shard-varying parameters and a vector of non-varying parameters.

What would be really great is a vector of non-varying integers. The reason is because with more complicated models, a number of parameters need to be passed to the function to determine what kind of model to run, etc. While it is possible to append these on to the varying integer, the code would be much cleaner/logical with a separate vector.

Example

map_rect(...., data int[] fixed_i, data real[] fixed_r)

Current Version:

v3.0.0

Start by tracing the current map_rect entry point and how its shard-varying integer and real arguments are handled. Done means map_rect supports fixed integer and real data shared across shards, matching the proposed argument shape in the example.