Standardize compression decoders' dictionary / history APIs

[nigeltao]

As of Wuffs v0.3, there is a base.io_transformer interface:

• set_quirk_enabled!(quirk: u32, enabled: bool)
• transform_io?(dst: io_writer, src: io_reader, workbuf: slice u8)
• workbuf_len() range_ii_u64

and every compression decoder is a base.io_transformer, but there isn't an additional base.compression_decoder interface. Instead, we have some ad hoc additional methods:

• deflate.decoder.add_history!(hist: slice u8)
• lzw.decoder.flush!() slice u8
• lzw.decoder.set_literal_width!(lw: u32[..= 8])
• zlib.decoder.add_dictionary!(dict: slice u8)
• zlib.decoder.dictionary_id() u32
• There's also the gzip.decoder struct, which doesn't export anything beyond the base.io_transformer methods.

It would be nice if there was a common API, at least for the dictionary / history concepts.