We have agreed that `agreeWithArgument` sounds more intuitive to localizers than
`agreeWithReplacement`. This attribute hasn't been adopted internally yet, so we
can afford to rename it just before the SDK freeze.
* rdar://107778676 Stop vendoring the Collections package
* rdar://107778676 Fix test expectation
AttributedString.CharacterView needs to round all indices down to the
nearest Character boundary to avoid semantic issues with its
Collection conformance. This means that CharacterView slices can never
start or end in between Character boundaries.
* Remove a stray print statement
