There is a new toolbar right above the layout editor canvas, which contains layout-related actions. The actual toolbar buttons shown depend on the current selection, as well as the layout parent of the selection. If you select a Button in a LinearLayout for example, you will see actions related to the LinearLayout, such as a toggle to switch between horizontal and vertical layout, and a toggle to control whether its children are aligned along their text baseline. You will also see toolbar actions to control the individual layout attributes of the child, such as whether it should stretch out to match its parent's width and height, a dropdown action to set its layout gravity, a button to open a margin editor, a layout weight editor, and so on.
The zoom controls, which used to be part of the configuration chooser, have also been moved into the layout actions bar, on the right hand side.