Optimize `checked_ilog` and `pow` when `base` is a power of two#147250

Kmeakin wants to merge 5 commits intorust-lang:mainrust-lang/rust:mainfrom

Kmeakin:km/optimize-ilog-base-power-of-twoKmeakin/rust:km/optimize-ilog-base-power-of-twoCopy head branch name to clipboard