[OE-core] what is MACHINE_HWCODECS used for these days?

[Robert P. J. Day]

  was documenting the use of [EXTRA_]IMAGE_FEATURES, and noticed that
while the oe-core layer defines a related feature:

  core-image.bbclass:FEATURE_PACKAGES_hwcodecs = "${MACHINE_HWCODECS}"
  core-image.bbclass:MACHINE_HWCODECS ??= ""

i see no actual usage of that variable in oe-core (the git log goes
way back to 2013:

  commit 1cb370587fd72e3f0f69678748108cc4116767fb
  Author: Richard Purdie <richard.purdie at linuxfoundation.org>
  Date:   Wed Jan 23 21:56:11 2013 -0800

    core-image: Add hwcodecs IMAGE_FEATURE

    Currently hardware codecs are being injected in rather ugly ways and end up
    either in no or all images. This adds a dedicated IMAGE_FEATURE for them based
    on the MACHINE_HWCODECS variable. We may need to refine this in due course
    but this patch at least illustrates the concept.

i looked through other layers on my system, and found some references
in meta-intel:

conf/machine/intel-core2-32.conf:MACHINE_HWCODECS ?= "intel-vaapi-driver gstreamer1.0-vaapi"
conf/machine/intel-corei7-64.conf:MACHINE_HWCODECS ?= "${@bb.utils.contains('TUNE_FEATURES', 'mx32', '', 'intel-media-driver
intel-mediasdk', d)} intel-vaapi-driver gstreamer1.0-vaapi"
conf/machine/intel-skylake-64.conf:MACHINE_HWCODECS ?= "intel-media-driver intel-mediasdk intel-vaapi-driver
gstreamer1.0-vaapi"

but i see nothing in *that* layer that actually does anything with
that variable after setting it. what is it used for? and how is it
processed?

rday