Collection extensions to get all possible prefixes in decreasing or increasing order of length

Collection+Prefixes.swift

public extension Collection {
	func contractingPrefixes() -> some Collection<SubSequence> {
		self.indices.reversed().lazy.map { index in
			self[startIndex ... index]
		}
	}
	
	func expandingPrefixes() -> some Collection<SubSequence> {
		self.indices.lazy.map { index in
			self[startIndex ... index]
		}
	}
}