Now that D75203 has landed and baked for a few days, extend the basic approach to prefix padding as well. The patch itself is fairly straight forward.
I did hit a small snag which is that we don't really have a good model for how many prefixes are safe to add with the current information. I'd planned to use the nop length information as a proxy, but it appears that this has never been updated for modern Intels. I haven't investigated to figure out why just yet.
For the moment, this patch adds the functional support and some basic testing there of, but defaults to not enabling prefix padding. I want to be able to phrase a separate patch which adds the target specific reasoning and test it cleanly. I haven't decided whether I want to common it with the nop logic or not.