[C++][IPC] Turn disabled bodyLength assertions into error checks #48844
Description
Describe the enhancement requested
In #19596 it was reported that the JavaScript IPC writer could produce inconsistent bodyLength values for the same IPC message in Message.bodyLength vs. Block.bodyLength in Arrow IPC files. It was subsequently fixed (all in September 2018, i.e. ~7 years ago).
Some corresponding assertions were added at the same point by @wesm but left disabled.
However, since the Javascript IPC writer bug was fixed so long ago, we now re-enable those assertions, or rather turn them into proper runtime errors.
Component(s)
C++