IntrinsicMeasureScope
What a layout function can do whether it is answering an intrinsic question or measuring: read its environment. Receiver for a LayoutFunction's intrinsic overrides, which answer a number: they may not measure, declare a size or place. MeasureScope adds measuring and declaring.
Nothing in Litho asks a layout function's intrinsic overrides yet: Yoga measures a Layout by running LayoutFunction.measure.
Sealed: only Litho provides one.