removing measurements: getIntersectionChangeEntry

[samouri]

Partial for #31540

• introduce helper Introduce measureIntersection helper for async measures. #31858
• LegacyIntersectionObserverHost Remove getChangeIntersectionEntry from LegacyAdIntersectionObserverHost #31693
• ads iframes: Convert ad iframes to get initialIntersection async #31753
• amp-video-iframe amp-video-iframe: use InOb instead of ce.getIntersectionChangeEntry. #31730
• amp-video manager: video-manager-impl: remove usage of getIntersectionChangeEntry #31942
• Rasta Experiment Remove sync measurement from ad iframes: experiment #32437
• remove from custom-element Remove .getIntersectionChangeElement from AMP CE. #37317