[SR-4538] [SE-153] Compensate for the inconsistency of @NSCopying's behaviour

[tkremenek]

Previous ID	SR-4538
Radar	rdar://problem/21383959
Original Reporter	@tkremenek
Type	Bug

Additional Detail from JIRA

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

md5: a17d921fd7c4fefbe3ada42983c8a199

Issue Description:

From SE-153:

"@NSCopying attribute does not work as consistently as we usually expected in Swift initializers after developers declared a property as @NSCopying."
...
"Do the compiler magic to call copy( with: ) in the initializer so that @NSCopying attribute no longer subjects to the fact that setter methods would not be invoked in initializers. Copying should always take place after a property has been declared as @NSCopying. It seems like the most direct way to maintain the @NSCopying contract without changing the underlying direct-storage model."

[tkremenek]

@swift-ci create