www/qt5-webengine: force build dependencies for pdf plugin (+)

Ensure to be all prerequisites built before pdf plugin build will be
started in same way as qt6-webengine already have done.
It affected at least aarch64 build.

www/qt5-webengine/files/patch-src_3rdparty_chromium_qtwebengine_browser_pdf_BUILD.gn

@@ -0,0 +1,9 @@
+--- src/3rdparty/chromium/qtwebengine/browser/pdf/BUILD.gn.orig	2025-04-23 16:00:55 UTC
++++ src/3rdparty/chromium/qtwebengine/browser/pdf/BUILD.gn
+@@ -7,5 +7,6 @@ source_set("pdf") {
+ 
+   deps = [
+     "//content/public/browser",
++    "//chrome/app:generated_resources",
+   ]
+ }