jco doesn't support wasmbuilder.app composed components with string parameter and return values about jco

[macovedj]

Some additional context. The repo linked in zulip has two components created using cargo-component. One is called hello, and just exposes a function that prepends a greeting string to an input name. This is imported by another component, big, which takes the greeting with the input name, and capitalizes all of the characters in the string, exporting this logic in a function called big_greet. The component linked in this issue is the result of using wasmbuilder to try and compose the components. The error message occurs when trying to use jco transpile on the result component.

panicked at 'not implemented', crates/js-component-bindgen/src/bindgen.rs:1029:49
(jsct transpile) RuntimeError: unreachable
    at __rust_start_panic (wasm://wasm/0122631e:wasm-function[3490]:0x1fdc92)
    at rust_panic (wasm://wasm/0122631e:wasm-function[3486]:0x1fdc3f)
    at _ZN3std9panicking20rust_panic_with_hook17h1e5f3993ce22fe2aE (wasm://wasm/0122631e:wasm-function[3485]:0x1fdc0f)
    at _ZN3std9panicking19begin_panic_handler28_$u7b$$u7b$closure$u7d$$u7d$17h757395b3caa1a881E (wasm://wasm/0122631e:wasm-function[3471]:0x1fcbd6)
    at _ZN3std10sys_common9backtrace26__rust_end_short_backtrace17h3e911ea98537fbdbE (wasm://wasm/0122631e:wasm-function[3470]:0x1fcb38)
    at rust_begin_unwind (wasm://wasm/0122631e:wasm-function[3480]:0x1fd866)
    at _ZN4core9panicking9panic_fmt17he9c46855d60d636eE (wasm://wasm/0122631e:wasm-function[3604]:0x206c27)
    at _ZN4core9panicking5panic17hf333278c14c20b5eE (wasm://wasm/0122631e:wasm-function[3610]:0x207190)
    at _ZN20js_component_bindgen7bindgen9JsBindgen11instantiate17hfe4cbb5545331156E (wasm://wasm/0122631e:wasm-function[101]:0xf8e0)
    at _ZN20js_component_bindgen9component8generate17h2fb6336405b47ca9E (wasm://wasm/0122631e:wasm-function[198]:0x280ae)

[guybedford]

I believe this is resolved with the transcoding support.