[SR-11963] FileManager.copyItem doesn't fail when there already is an item at destination path

[hartbit]

Previous ID	SR-11963
Radar	rdar://problem/58438122
Original Reporter	@hartbit
Type	Bug

Additional Detail from JIRA

Votes	0
Component/s	Foundation
Labels	Bug
Assignee	None
Priority	Medium

md5: 2e9a79d0bfa43aa0e8f648c528915c3f

Issue Description:

On Darwin, FileManager.copyItem fails when there is already a file or folder at the destination path. CLF doesn't exhibit the same behavior.

[beccadax]

@swift-ci create

[spevans]

Is this failing on Linux or Darwin? Do you have an example of the failure? The only reason I ask is that there is a test case for this scenario in the swift-corelibs-foundation unit tests and it throws an error correctly on both Darwin Foundation and scl-foundation.