Customize WASM initialization code

By default, this library injects its own initialization code to facilitate panic information recovery using console_error_panic_hook. If you would like to run some initialization code for WASM, e.g. to set up logging libraries, specify default-features = false in Cargo.toml:

flutter_rust_bridge = { version = "..", default-features = false, features = [..] }

The wasm-start feature governs this behavior and is enabled by default.