gimp: reenable avif/heic

libheif commit cf0d89c6e0809427427583290547a7757428cf5a removes the definitions
for the `builtin_h265_decoder`, `builtin_h265_encoder`, `builtin_avif_decoder`,
and `builtin_avif_encoder` pkg-config variables. This commit is included in
libheif 1.80.0 and newer. gimp 2.10.38 depends on these pkg-config variables in
its autoconf morass, and as a result is built without support for importing or
exporting avif and heic. This commit "fixes" this by forcefully setting these
feature detection flags to "yes" if any version of libheif is present.
Technically this logic should only apply to libheif 1.80.0 and above, but I
don't think there's really any good reason to bother with that additional
complication for a patch meant specifically for compiling gimp in a rolling
release distribution.

Some links:
 - <https://www.github.com/strukturag/libheif/issues/758>
 - <https://gitlab.gnome.org/GNOME/gimp/-/issues/9080>

srcpkgs/gimp/patches/libheif-1.18-compat.patch

@@ -0,0 +1,20 @@
+--- a/configure.ac	2024-08-29 18:28:19.457012043 -0500
++++ b/configure.ac	2024-08-29 18:28:29.154953488 -0500
+@@ -1843,13 +1843,13 @@
+ can_import_avif=no
+ can_export_avif=no
+ if test "x$have_libheif" = xyes; then
+-  can_import_heic=`$PKG_CONFIG --variable=builtin_h265_decoder libheif`
+-  can_export_heic=`$PKG_CONFIG --variable=builtin_h265_encoder libheif`
++  can_import_heic=yes
++  can_export_heic=yes
+   if test "x$can_import_heic" = xyes; then
+     MIME_TYPES="$MIME_TYPES;image/heif;image/heic"
+   fi
+-  can_import_avif=`$PKG_CONFIG --variable=builtin_avif_decoder libheif`
+-  can_export_avif=`$PKG_CONFIG --variable=builtin_avif_encoder libheif`
++  can_import_avif=yes
++  can_export_avif=yes
+   if test "x$can_import_avif" = xyes; then
+     MIME_TYPES="$MIME_TYPES;image/avif"
+   fi

srcpkgs/gimp/template

@@ -1,7 +1,7 @@
 # Template file for 'gimp'
 pkgname=gimp
 version=2.10.38
-revision=2
+revision=3
 build_style=gnu-configure
 configure_args="--disable-check-update --datadir=/usr/share --disable-python"
 hostmakedepends="automake gegl gettext-devel glib-devel gtk+-devel intltool