Add Vector.build_multiple and handle dataflow error and warning propagation in build and build_multiple

[GregoryTravis]

Adds Vector.build_multiple to build multiple Vectors at the same time.
Also handles uncaught dataflow errors being added to builders or returned from builder callbacks, as well as attached warning propagation.
This converts the remaining uses of Vector.new_builder to Vector.build in Standard.Base.

Following @Jaroslav’s suggestion, this PR implements the propagation of dataflow errors passed to Builder.append by wrapping them in a Panic.

This is implemented as Panic.throw_wrapped_if_error and Panic.handle_wrapped_dataflow_error, which I have modified to allow specifying the error type and a custom handler.

Previously, we relied on the dataflow errors being propagated by Builder.append, which sometimes required the fold pattern to ensure that error values were not added to the Builder as if they were regular values.

Checklist

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• The documentation has been updated, if necessary.
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[radeusgd]

Reconciling the very functional dataflow error and warning mechanisms with these rather-imperative builders is quite a challenge. I'm really really happy we are patching the holes and making the error/warning propagation more robust - that's really great!

I've got some minor comments. The biggest issue I see is the quadratic complexity explosion at warnings handling.

Maybe we should consider changing our underlying data structures, to make + on vectors more efficient (we could use a similar Rope structure as we use on the Text type). But that's a bigger effort. For now let's just (slightly ironically) use an imperative builder there.

[radeusgd]

Why is this slice needed here?

[GregoryTravis]

Previously this was needed to prevent an error, but it's not happening now, so I've removed it.