Document and validate that aWSM generated *.bc is a WASI module

[bushidocodes]

aWsm has added support for modules outside of the WASI spec. For example, modules that do not use the linear memory. However, SLEdge seems to be more opinionated around WASI, and it is unclear to me if supporting non-WASI WebAssembly targets has any particular value.

Our documentation should clarify our assumptions around WASI symbols. We should also validate these symbols during dlopen at runtime startup.