try to fix js_name error when both getter and setter used

[a1trl9]

Related to #2072

The error may come from Line 492 in codegen.rs:

        (quote! {
            #(#attrs)*
            #[allow(non_snake_case)]
            #[cfg_attr(
                all(target_arch = "wasm32", not(target_os = "emscripten")),
                export_name = #export_name, // this line...
            )]
            #[allow(clippy::all)]
            pub extern "C" fn #generated_name(#(#args),*) -> #projection::Abi {
                #start_check
                // Scope all local variables to be destroyed after we call the
                // function to ensure that `#convert_ret`, if it panics, doesn't
                // leak anything.
                let #ret = {
                    #(#arg_conversions)*
                    #receiver(#(#converted_arguments),*)
                };
                #convert_ret
            }
        })
        .to_tokens(into);

When both getter and setter are used, a name conflict occurs since export_name for both are the same.

[alexcrichton]

Thanks! Could a test be added for this as well?

[a1trl9]

@alexcrichton 6 tests added for wasm::getters_and_setters as follows:
8 - no getter/setter field name, same js_name, different rust name.
9 - no getter/setter field name, same js_name, same rust name (except set prefix).
10 - same getter/setter field name, same js_name, different rust name.
11 - different getter/setter field name, samd js_name, different rust name.
12 - same getter/setter field name, same js_name, same rust name (except set prefix).
13 - different getter/setter field name, samd js_name, same rust name (except set prefix).