fix(ext/ffi): improve error messages in FFI module (denoland#16922)

[mmastrac]

Fixes #16922.

The error messages in the ffi module are somewhat cryptic when passing functions that have invalid parameters or result type strings. While the generated serializer for the ForeignFunction struct correctly outputs a correct and verbose message, the user sees a far less helpful data did not match any variant message instead.

The underlying cause appears to be the fallback message in the auto-derived deserializer for untagged enums [1] generated as a result of ForeignSymbol being marked as #[serde(untagged)] [2]. Passing an unexpected value for NativeType causes it to error out while attempting to deserialize both enum variants -- once because it's not a match for the ForeignStatic variant, and once because the ForeignFunction deserializer rejects the invalid type for the parameters/return type. This is currently open as serde #773, and not a trivial exercise to fix generically.

[1] https://github.com/serde-rs/serde/blob/v0.9.7/serde_derive/src/de.rs#L730
[2] https://github.com/denoland/deno/blob/main/ext/ffi/dlfcn.rs#L102
[3] serde-rs/serde#773

Note that the auto-generated deserializer for untagged enums uses a private API to buffer deserializer content that we don't have access to. Instead, we can make use of the serde_value crate to buffer the values. This can likely be removed once the official buffering API lands (see [4] and [5]). In addition, this crate pulls in serde_json as a cheap way to test that the deserializer works properly.

[4] serde-rs/serde#741
[5] serde-rs/serde#2348

[CLAassistant]

All committers have signed the CLA.

[littledivy]

LGTM, thank you!