Encoding parameters inconsistently duplicated between Encoder and Info

[Shnatsel]

As of v0.17.14, some encoding parameters are duplicated between the Info struct and the Encoder struct.

For example, Info has the compression field, but not filter or adaptive_filter. The presence of Info::compression is especially strange because e.g. StreamingDecoder::info() returns an instance of Info but it has no way to know what the compression level originally was, so I have no idea what it's even supposed to return in that case.

[fintelia]

The Info struct should only hold metadata. We should probably deprecate the compression field and do all tracking of compression settings directly on the Encoder

A followup question is whether we should think about lazy loading of metadata and what the API for that might look like.