[gdk-pixbuf] (12 commits) ...Merge branch 'ebassi/for-master' into 'master'

[Emmanuele Bassi <ebassi src gnome org>]

Summary of changes:

  437cc45... Use 'provide' section in libpng wrap file (*)
  6bd142f... Install API reference under $datadir/doc (*)
  f265a94... build: Use a dict for pkg-config file variables (*)
  caa93d9... ci: Update the version of Meson (*)
  949a9b9... build: Use more idiomatic Meson (*)
  117cc8b... build: Handle -Dbuiltin_loaders=none (*)
  a6175b6... Build PNG and JPEG loaders into gdk-pixbuf by default (*)
  6e8a9c6... build: Change the default for builtin_loaders (*)
  866670e... build: Port post-install script to Python (*)
  dac7bba... build: Use `type:array` for builtin_loaders option (*)
  a3bc66a... build: Use a dict for loader data (*)
  09ebed7... Merge branch 'ebassi/for-master' into 'master'

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