[gnome-software] (15 commits) ...Merge branch 'wip/mak/libas' into 'master'

[Philip Withnall <pwithnall src gnome org>]

Summary of changes:

  f749a1d... build: Disable building libmalcontent-ui in subprojects (*)
  6d4e67d... Add Meson wrap file for AppStream (*)
  06f3100... meson: Adjust dependency for AppStream, replacing appstream (*)
  d6e1250... Adjust CI dependencies for AppStream (*)
  747708a... ci: Add dependencies for appstream subproject to CI Dockerf (*)
  1364588... Port to appstream (*)
  d99f3ca... Delete defunct remnants of shell-extension support (*)
  2966054... Use separate enum for OS update pseudo-apps (*)
  5f3466e... Replace AS_URL_KIND_MISSING with explicit property (*)
  476544f... trivial: Suggest using appstreamcli for NEWS/validate (*)
  1273aba... Transparently convert 6-part data-ids to 5-part IDs in publ (*)
  cc0d0fa... Parse all provided item types properly (*)
  484912c... ci: Use CI images which contain cached appstream subproject (*)
  f61d690... build: Use C11 standard (*)
  d8a41f0... Merge branch 'wip/mak/libas' into 'master'

(*) This commit already existed in another branch; no separate mail sent