dev-qt/qtwebengine: enable pdfium by default in live (qt6)

Formerly left disabled given nothing in the tree needed it and it was
just an oddity, but some packages started to use it now (skanpage and
upcoming frescobaldi bump through pyqt6) and it is annoying to find
out that you need to rebuild qtwebengine to enable it.

It does add a bit to the compile time and size making it wasteful for
"most" users but it is ultimately kind of negligible in relation to
webengine itself.

Doing it live-only to spare a rebuild, will be for next bump.

Signed-off-by: Ionen Wolkens <ionen@gentoo.org>

dev-qt/qtwebengine/qtwebengine-6.8.9999.ebuild

@@ -19,7 +19,7 @@ fi
 
 IUSE="
 	accessibility +alsa bindist custom-cflags designer geolocation
-	+jumbo-build kerberos opengl pdfium pulseaudio qml screencast
+	+jumbo-build kerberos opengl +pdfium pulseaudio qml screencast
 	+system-icu vaapi vulkan webdriver +widgets
 "
 REQUIRED_USE="

dev-qt/qtwebengine/qtwebengine-6.9.9999.ebuild

@@ -19,7 +19,7 @@ fi
 
 IUSE="
 	accessibility +alsa bindist custom-cflags designer geolocation
-	+jumbo-build kerberos opengl pdfium pulseaudio qml screencast
+	+jumbo-build kerberos opengl +pdfium pulseaudio qml screencast
 	+system-icu vaapi vulkan webdriver +widgets
 "
 REQUIRED_USE="

dev-qt/qtwebengine/qtwebengine-6.9999.ebuild

@@ -1,4 +1,4 @@
-# Copyright 2021-2024 Gentoo Authors
+# Copyright 2021-2025 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2
 
 EAPI=8
@@ -19,7 +19,7 @@ fi
 
 IUSE="
 	accessibility +alsa bindist custom-cflags designer geolocation
-	+jumbo-build kerberos opengl pdfium pulseaudio qml screencast
+	+jumbo-build kerberos opengl +pdfium pulseaudio qml screencast
 	+system-icu vaapi vulkan webdriver +widgets
 "
 REQUIRED_USE="