package/gstreamer1/gst1-plugins-base: convert package type to meson

package/gstreamer1/gst1-plugins-base: convert package type to meson

GStreamer 1.16.0 is the last version to support autotools, which is
removed in the next version.

Other changes:
  - The meson build provides no 'disable-valgrind' option in the plugin
    packages (valgrind availability checking is done in the base
    gstreamer package already).

  - zlib no longer has an option and is also checked via headers.

  - Add the following new meson-specific options:
  - -Dgtk_doc=disabled
  - -Dglib-asserts=disabled
  - -Dglib-checks=disabled
  - -Dgobject-cast-checks=disabled

  - Three config options are comma separated strings. These
    options are:
      - gl_api
      - gl_platform
      - gl_winsys

    The lists can be passed empty without error. As such, the logic now
    creats a list such as:
    -Dgl_api='opengl,gles2'
    -Dgl_platform='glx,egl'
    -Dgl_winsys='x11,wayland'

  - Remove the egl BASE_CONF_ENV CPPFLAGS and LIBS options, as meson finds
    the include paths and libraries correctly during the configure stage.

Signed-off-by: Adam Duskett <Aduskett@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>