Add support for sized lists: `list<u8, 4>`

[mkatychev]

from the WIT design doc:

🔧 A list with a fixed length provides the low-level memory representation of a homogeneous tuple of the same length, but with the dynamic indexing of a list. E.g., the following two functions have the same low-level (Core WebAssembly) representation, but will naturally produce different source-level bindings:

get-ipv4-address1: func() -> list<u8, 4>;
get-ipv4-address2: func() -> tuple<u8, u8, u8, u8>;