Android P DP2 brings a rotation lock button to the Pixel Launcher which, if you've got a device with the Pixel launcher installed that's capable of running on the second developer preview of Android P, you may have already noticed the button's appearance, that is assuming you have the software installed in the first place. As of right now there are a handful of devices which are compatible with the Android P developer preview 2 software, some of which will have to wait for the update to be pushed out over-the-air as part of the beta program that Google announced today during its I/O 2018 developer conference, some which will be able to flash the software right away as part of the system images that Google just put out.
The new button will appear if you rotate your device while on the home screen if you have the auto-rotate feature disabled, which makes it a nifty tool to have should you want to get your phone's home screen into landscape mode and lock it into place. If you get the second dev preview of Android P installed you may also notice app actions showing up in the Pixel launcher as well. App actions were announced earlier today during Google's keynote, and are supposed to predict the user's behavior at the right time based on use and learned details.
App actions are already popping up in the pixel Launcher's app drawer and should be sitting just above the first app in the drawer but below the search bar, if there are any actions that the launcher feels it needs to suggest at the time. If you're using the Pixel launcher then these will give you quick little way to jump to a certain app, and since the actions are powered by AI they should change from time to time, so they won't always be the same and should be based on your use.