Will we support Decimal128Array?

[sffc]

It would be really nice to interoperate directly with WebAssembly by reading and writing these to array buffers.

I think doing so would probably require support for cohorts / precision? #175

[littledan]

I'd like to procrastinate on this (for a future proposal), given that there are multiple binary representation conventions for decimals (separate from cohorts and endianness). Let's see if it's a widely demanded feature. I don't think it is.