Draft: PREVIEW: audio: take advantage of package name to avoid type and const name redundancy

This is a preview for how code would look like with gstreamer-rs#374 (closed). Only plugins under audio are affected in this preview. This is because I only changed gst_base & gst_audio so far. See this branch.

This is based on gir changes from this branch:

• A "removable prefix" is determined based on each namespace specificities: if the first symbol prefix (e.g. gst, from the gir file namespace attribute c:symbol-prefixes) matches the first part of the crate name (e.g. gst_audio), then all functions starting with audio_, all types starting with Audio and all constants starting with AUDIO_ will get their prefix removed...

• ... unless Gir.toml instructs otherwise (just to show how this could be fine-tuned):

  • Disabling for all types in a namespace

    [[object]]
    name = "GstApp.*"
    removable_prefix = "disabled"

  • Disabling for a specific type only

    [[object]]
    name = "GstBase.BaseSink"
    removable_prefix = "disabled"

  • Disabling for all constants

    [[object]]
    name = "GstGL.*"
    [..]
        [[object.constant]]
        pattern = "*"
        removable_prefix = "disabled"

  • Disabling for a specific constant only

    [[object]]
    name = "GstGL.*"
    [..]
        [[object.constant]]
        name = "GL_API_GLES1_NAME"
        removable_prefix = "disabled"

  • Forcing for all types in a namespace

    [[object]]
    name = "GstRtspServer.*"
    removable_prefix = "RTSP"

  • and so on...

• I also removed the prefix from generated and manual source filenames. This leads to shorter paths and use clauses. E.g.:

  use gst_base::subclass::transform::GenerateOutputSuccess;

  See this FIXME for an unrelated proposal about this particular use clause, and this other FIXME for a similar proposal.

• However, I kept the traits prefix to avoid conflicts when used with a prelude::* clause. So we still have BaseSinkExt and AudioBaseSinkExt for instance.