[LORO-345] Reduce WASM size by reduce the use of generic in rich text

[zxch3n]

Avoid the usage like this:

        let (c, entity_index) = match pos_type {
            PosType::Bytes => todo!(),
            PosType::Unicode => self.find_best_insert_pos::<UnicodeQueryT>(pos),
            PosType::Utf16 => self.find_best_insert_pos::<Utf16QueryT>(pos),
            PosType::Entity => self.find_best_insert_pos::<EntityQueryT>(pos),
            PosType::Event => self.find_best_insert_pos::<EventIndexQueryT>(pos),
        };

_{From SyncLinear.com | LORO-345}