Function generate_subdecoder_flat_dispatch 

pub fn generate_subdecoder_flat_dispatch(
    sd: &ValidatedSubDecoder,
    handler_mod: &str,
    ctx_type: &str,
    groups: &HashMap<String, String>,
    instr_type: Option<&str>,
    invalid_handler: Option<&str>,
    strategy: Dispatch,
) -> Result<String, Vec<Error>>

Generate a flat dispatch function for a sub-decoder. Uses the explicit flat_lut or flat_match strategy. Errors on raw-value ambiguity.