Introduce the videoconvertscale element
Now that videoconvert and videoscale's are both based on GstVideoConverter and are using the exact same code, it makes much more sense to have one element doing the two operation, and it can be more efficient in some cases (one single path for both operations).
This removes the
videoconvert plugins but keeps the element
making them also do both operations (adding some APIs to each element).
There is a small change in API for the
videoscale:dither property which
was previously a totally unused boolean, it is now an enum and is used.