gdk/broadway/toarray.pl: Fix Code Generation for MSVC

The current implementation of this script generate headers with \x-escaped
strings that can become too long (> 65535 characters) for Visual Studio
to consume, hence the build of broadwayd would break on Visual Studio.

This changes the script to instead format the string as an array of hex
characters, not unlike what GResource does, so that builds can continue as
normal on Visual Studio builds as well.

https://bugzilla.gnome.org/show_bug.cgi?id=739001