Add support for multi memory

[liangzhupic]

I noticed that the multi-memory proposal is going to be the phase 4 currently. Refer to multi-memory-phase4 .Will wasm micro runtime team add support for this new feature which is useful for the use case that import a host mmap memory to wasm instance to access it. I'm looking forward it.

[wenyongh]

Hi, it is really useful if multi-memory can help share buffer between two wasm modules, but for the toolchain, it seems that only binaryen supports it, right? And not sure how to leverage this feature when writing the wasm app (e.g. C/C++/Rust), is there any case (like importing a host mmap memory as you mentioned)?