RFC: take advantage of package name to shorten types name

When writing a plugin or an application, it is quite common to use e.g. gst_audio::AudioFormat, which appears redundant.

This RFC proposes to avoid name redundancy when the package name already gives context. Of course this would be a general guideline, there are probably specific cases where this wouldn't help.

In the above example, we would use gst_audio::Format instead. If users really want to import the type, they could still pull it in scope like this:

use gst_audio::Format as AudioFormat;

Another related example is the native endians aliases, which are named gst_audio::AUDIO_FORMAT_.... These must be used with the gst_audio:: prefix anyway, unless the user pulled them in scope with use gst_audio::*.