Check function arguments in IPROTO

IPROTO doesn't check arguments passed to a function executed with IPROTO_CALL. This is supposed to be done by the function implementation, but doing it in the main thread may negatively affect performance. It'd be nice if this job could be offloaded to IPROTO threads, because the number of IPROTO threads is configurable and typically they are less loaded than the transaction processing thread.

Now, that we have box.iproto.export() (#10036), we can pass the arguments schema to it when exporting a function. The schema could be "compiled" and passed to IPROTO, where function arguments would be checked against it. We could also verify the return value and raised errors in the "debug" mode.

See also #11760.

Start by reviewing the existing box.iproto.export() behavior from #10036 and the IPROTO_CALL path described here, then compare the related discussion in #11760. Define how an exported function's argument schema reaches IPROTO threads and how validation, including optional debug-mode return and error checks, should be verified.