Macro gen_class_name

macro_rules! gen_class_name {
    ($single_part_class:ident $($param_name:ident)?) => { ... };
    ($($class:ident).+ $($param_name:ident)?) => { ... };
    (@inner $last:ident) => { ... };
    (@inner $first:ident . $($rest:ident).+) => { ... };
}

Generate the dot separated java class name to the slash separated name.

assert_eq!(
    "java/lang/String",
    risingwave_jni_core::gen_class_name!(java.lang.String)
);
assert_eq!(
    "java/lang/String",
    risingwave_jni_core::gen_class_name!(String)
);