build/linux: Fix AVIF, HEIC and J2K support on Snap package

The GNOME SDK Snap have only AVIF and HEIC decoding plugins,
no AVIF or HEIC encoding plugins and no J2K at all. So,
let's complete the support with 'build-packages:'.

build/linux/snap/snapcraft.yaml

@@ -38,6 +38,8 @@ apps:
       LD_LIBRARY_PATH: $SNAP/usr/lib/$CRAFT_ARCH_TRIPLET_BUILD_FOR/blas:$SNAP/usr/lib/$CRAFT_ARCH_TRIPLET_BUILD_FOR/lapack:$LD_LIBRARY_PATH
       #JavaScript plug-ins support
       GI_TYPELIB_PATH: $SNAP/gnome-platform/usr/lib/$CRAFT_ARCH_TRIPLET_BUILD_FOR/gjs/girepository-1.0:$GI_TYPELIB_PATH
+      #AVIF, HEIC and J2K plug-ins support
+      LIBHEIF_PLUGIN_PATH: $SNAP/usr/lib/$CRAFT_ARCH_TRIPLET_BUILD_FOR/libheif/plugins
     slots:
       - dbus-gimp
     plugs:
@@ -153,7 +155,6 @@ parts:
       - libexpat1-dev #it is on Gnome SDK Snap but inexplicably the linker can't find it
       - libgexiv2-dev
       - libgs-dev
-      - libheif-dev
       - libjxl-dev #https://github.com/ubuntu/gnome-sdk/issues/317
       - libmng-dev
       - libmypaint-dev
@@ -165,7 +166,12 @@ parts:
     stage-packages:
       - libgexiv2-2
       - libgs10
-      - libheif1
+      - libheif-plugin-dav1d
+      - libheif-plugin-aomenc
+      - libheif-plugin-libde265
+      - libheif-plugin-x265
+      - libheif-plugin-j2kdec
+      - libheif-plugin-j2kenc
       - libmng2
       - libmypaint-1.5-1
       - libwmf-0.2-7