Add `bit_array.to_string_utf16` and `to_string_utf32`

[GearsDatapacks]

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Some binary protocols (for example ID3) use UTF-16 encoded text, which right now must be manually converted to a string. It could be useful to have bit_array.to_string_utf16 function to perform this conversion. to_string_utf32 is not something that I've personally needed, but could be useful as well.

Additionally it could be helpful to be able to specify endianness as that is something which varies across standards.