gstreamer: 1.16.2 -> 1.18.0

Fixes #98769.

Important changes from https://gstreamer.freedesktop.org/releases/1.18/:

* `gst-validate` was renamed to `gst-devtools` upstream:

    > * the `gst-validate` tarball has been superseded by
    >   the `gst-devtools` tarball for consistency with the git module name.

* `gst-python` is now Python 3 only:

    > * Python 2.x is no longer supported

pkgs/development/libraries/gstreamer/devtools/default.nix

@@ -0,0 +1,62 @@
+{ stdenv
+, fetchurl
+, meson
+, ninja
+, pkgconfig
+, gstreamer
+, gst-plugins-base
+, python3
+, gobject-introspection
+, json-glib
+}:
+
+stdenv.mkDerivation rec {
+  pname = "gst-devtools";
+  version = "1.18.0";
+
+  src = fetchurl {
+    url = "${meta.homepage}/src/${pname}/${pname}-${version}.tar.xz";
+    sha256 = "05jzjkkdr5hg01mjihlqdcxqnjfrm4mqk0zp83212kv5nm0p2cw2";
+  };
+
+  patches = [
+    ./fix_pkgconfig_includedir.patch
+  ];
+
+  outputs = [
+    "out"
+    "dev"
+    # "devdoc" # disabled until `hotdoc` is packaged in nixpkgs
+  ];
+
+  nativeBuildInputs = [
+    meson
+    ninja
+    pkgconfig
+    gobject-introspection
+
+    # documentation
+    # TODO add hotdoc here
+  ];
+
+  buildInputs = [
+    python3
+    json-glib
+  ];
+
+  propagatedBuildInputs = [
+    gstreamer
+    gst-plugins-base
+  ];
+
+  mesonFlags = [
+    "-Ddoc=disabled" # `hotdoc` not packaged in nixpkgs as of writing
+  ];
+
+  meta = with stdenv.lib; {
+    description = "Integration testing infrastructure for the GStreamer framework";
+    homepage = "https://gstreamer.freedesktop.org";
+    license = licenses.lgpl2Plus;
+    platforms = platforms.unix;
+  };
+}

pkgs/development/libraries/gstreamer/devtools/fix_pkgconfig_includedir.patch

@@ -0,0 +1,15 @@
+diff --git a/validate/pkgconfig/meson.build b/validate/pkgconfig/meson.build
+index a612b21b..c017eaff 100644
+--- a/validate/pkgconfig/meson.build
++++ b/validate/pkgconfig/meson.build
+@@ -2,8 +2,8 @@ pkgconf = configuration_data()
+
+ pkgconf.set('prefix', get_option('prefix'))
+ pkgconf.set('exec_prefix', '${prefix}')
+-pkgconf.set('libdir', '${prefix}/@0@'.format(get_option('libdir')))
+-pkgconf.set('includedir', '${prefix}/@0@'.format(get_option('includedir')))
++pkgconf.set('libdir', join_paths(get_option('prefix'), get_option('libdir')))
++pkgconf.set('includedir', join_paths(get_option('prefix'), get_option('includedir')))
+ pkgconf.set('GST_API_VERSION', apiversion)
+ pkgconf.set('VERSION', gst_version)
+