wit-dylib: Generate helper functions during lifting/lowering

Right now each adapter generates one monolithic wasm function per world import and world export. This means that if a `list` is used many times, it'll have duplicated lowering/lifting code in many places. Should consider splitting out helpers to, for example, read `T` from linear memory (or write it) and delegate to those helpers instead. Some discussion [here](https://github.com/bytecodealliance/wasm-tools/pull/2304#pullrequestreview-3230168549) about this too.