[SR-7266] reversed() applied multiple times should not nest ReversedCollection into itself

[moiseev]

Previous ID	SR-7266
Radar	None
Original Reporter	@moiseev
Type	Improvement
Status	Resolved
Resolution	Done

Additional Detail from JIRA

Votes	0
Component/s	Standard Library
Labels	Improvement, StarterBug
Assignee	@Moximillian
Priority	Medium

md5: d7a13ecbc1a535d769141383adecf60a

Issue Description:

Right now applying reversed() twice will result in a ReversedCollection<ReversedCollection<Base>>.

(swift) [1,2].lazy.reversed()
// r0 : LazyCollection<ReversedCollection<[Int]>> = Swift.LazyCollection<Swift.ReversedCollection<Swift.Array<Swift.Int>>>(_base: Swift.ReversedCollection<Swift.Array<Swift.Int>>(_base: [1, 2]))
(swift) r0.reversed()
// r1 : LazyCollection<ReversedCollection<ReversedCollection<[Int]>>> = Swift.LazyCollection<Swift.ReversedCollection<Swift.ReversedCollection<Swift.Array<Swift.Int>>>>(_base: Swift.ReversedCollection<Swift.ReversedCollection<Swift.Array<Swift.Int>>>(_base: Swift.ReversedCollection<Swift.Array<Swift.Int>>(_base: [1, 2])))
(swift) [1].reversed()
// r2 : ReversedCollection<[Int]> = Swift.ReversedCollection<Swift.Array<Swift.Int>>(_base: [1])
(swift) r2.reversed()
// r3 : ReversedCollection<ReversedCollection<[Int]>> = Swift.ReversedCollection<Swift.ReversedCollection<Swift.Array<Swift.Int>>>(_base: Swift.ReversedCollection<Swift.Array<Swift.Int>>(_base: [1]))

I believe we can be smarter and avoid this nesting.

[Moximillian]

The regular (non-lazy) version fixed in #15815

[Moximillian]

lazy version fixed in the PR, by adding ReversedCollectionProtocol

[moiseev]

Merged the non-lazy variant here: 02aef12

Lazy version is harder to implement without extra protocols or new compiler features, so not doing it for now.