Add conversions for YUY2 (YUYV) encoding

[sgvandijk]

In ros2/common_interfaces#78 the yuv422_yuy2 image encoding was added, which is the format commonly coming out of webcams.

This PR adds conversions from this format, in line with the existing yuv422 ones for UYVY.

[mjcarroll]

@ros-pull-request-builder retest this please

[sgvandijk]

I guess this is blocked until common_interfaces makes a new release, which seems to be 1.0 as tracked in ros2/common_interfaces#84

[threeal]

it has been a long time, when will it going to be released?

[HorvathDawson]

Should we expect this to be released soon?

[sgvandijk]

The sensor_msgs packages which defines the required image format has now been released and is available for Focal. I've rebased to test with the latest versions and it looks like it now compiles fine with Foxy/Focal, not with Dashing/Bionic as expected. @mjcarroll should I try to make it backward compatible (not sure how) or is this fine?

[russkel]

Thanks for work on this @sgvandijk. Useful since the raspberry pi camera modules only seem to be ROS1.

[sgvandijk]

@mjcarroll I've rebased to latest ros2 again. It'd be great if this can get in so we can finally release the integration of cv_bridge in the V4L2 camera driver.

[russkel]

You might want to take out bionic of the CI testing in this branch?

[mjcarroll]

Superceded by #396