Add JPEG 2000 decoding support

[Enet4]

This adds direct support for decoding pixel data in JPEG 2000, via jpeg2k. jpeg2k lets us pick between linking the reference implementation of OpenJPEG (Cargo feature openjpeg-sys) or a Rust port (Cargo feature openjp2).

A few more changes were made to the Cargo feature set so that downstream crates can be more specific about which via dicom-pixeldata. For instance, doing cargo install --path toimage would include the Rust port of openjp2, but with the command below, you can build dicom-toimage statically linked with the OpenJPEG reference software.

cargo install --path toimage --no-default-features \
    --features=dicom-pixeldata/jpeg,dicom-pixeldata/rle,dicom-pixeldata/openjpeg-sys

Summary

• [ts-registry] add features openjp2 and openjpeg-sys
  • they map to the backend impl of JPEG 2000 via jpeg2k
• [ts-registry] add JPEG 2000 pixel data adapter with decoding support
• [pixeldata] expose more transfer-syntax-registry features, so that specific image decoding implementations can be selected
• [pixeldata] adjust jpeg decoding test cases according to support
• [toimage] relocate dicom-pixeldata/native to default features, so that native implementations can be disabled at will