Treat Bytes in ProspectingTexture#map as UByte & switch to fastutil maps

[MCTian-mi]

What

Fixes an oversight in #2726, where Bytes in ProspectingTexture#map aren't treated as unsigned as intended, resulting MCTian-mi/SussyPatches#32, where the same feature was implemented for 2.8.10.

Also replaced original HashMap<Byte, String>s with Byte2ObjectOpenHashMaps from fastutil.

Implementation Details

Replaced the Byte#intValue method call with Byte#toUnsignedInt, whose implementation is:

    /**
     * Converts the argument to an {@code int} by an unsigned
     * conversion.  In an unsigned conversion to an {@code int}, the
     * high-order 24 bits of the {@code int} are zero and the
     * low-order 8 bits are equal to the bits of the {@code byte} argument.
     *
     * Consequently, zero and positive {@code byte} values are mapped
     * to a numerically equal {@code int} value and negative {@code
     * byte} values are mapped to an {@code int} value equal to the
     * input plus 2<sup>8</sup>.
     *
     * @param  x the value to convert to an unsigned {@code int}
     * @return the argument converted to {@code int} by an unsigned
     *         conversion
     * @since 1.8
     */
    public static int toUnsignedInt(byte x) {
        return ((int) x) & 0xff;
    }