Macro multi_byte_tests

macro_rules! multi_byte_tests {
    (@shared dups=[$($dups:pat),* $(,)*]) => { ... };
    (
        dups = [$($dups:pat),* $(,)*]
    ) => { ... };
    (
        remap = [$remap_min:expr, $remap_max:expr],
        dups = [$($dups:pat),* $(,)*]
    ) => { ... };
}

Makes a common test suite for multi-byte indices.