This adds `-wasm-enable-exnref`, which will enable the new EH instructions using `exnref` (adopted in Oct 2023 CG meeting): https://github.com/WebAssembly/exception-handling/blob/main/proposals/exception-handling/Exceptions.md This option should be used with `-wasm-enable-eh`.
This adds tests for EH/SjLj option errors and swaps the error checking order for unimportant cosmetic reasons (I think checking EH/SjLj conflicts is more important than the model checking)