Add DW_FEATURE_TREE feature test, since iOS does not suppor tree. Update dwtest to show a placeholder when missing the tree widget. Remove DW_FEATURE_CONTAINER_STRIPE from GTK4. Apparently it is supported with the GtkListBox widget and custom CSS, but it performs badly and is unrecommended by the GTK development team. Finally add missing feature test example code to the template source.

prefix=@prefix@
exec_prefix=${prefix}
libdir=${exec_prefix}/lib
includedir=${exec_prefix}/include
 
Name: dwindows
Description: Dynamic Windows Cross platform UI Toolkit
Version: @VERSION@
Libs: -L${prefix}/lib -ldwindows @LIBS@
Cflags: -I${prefix}/include @CFLAGS@ -D@DW_DEFINE@