Span: Remove ownership modifiers and explicit copies from pointers.

[atrick]

Without this fix, the standard library source will break with shortly upcoming compiler toolchain.

Never explicitly copy a pointer before passing it to an argument that is the source of a lifetime dependency on the function's return value. That will always raise a diagnostic error: depending on a temporary value is not the same as depending on a variable. A temporary value's scope is only the current expression.

Also avoid using ownership modifiers for UnsafePointer. We don't want to treat them like noncopyable types. They are simply values. Treating them like noncopyable types creates a lot of overhead in the representation, which is likely to interfere with diagnostics and optimization.

[atrick]

@swift-ci test

[atrick]

BitwiseCopyable appears to be broken for UnsafeBufferPointer. I'm seeing this diagnostic, which never triggers for BitwiseCopyable types:

error: invalid use of borrow dependence with consuming ownership
extension Swift.Span where Element : ~Copyable {
   #if compiler(>=5.3) && $LifetimeDependence
   @lifetime(borrow buffer)
                    `- error: invalid use of borrow dependence with consuming ownership
   @_alwaysEmitIntoClient public init(_unsafeElements buffer: Swift.UnsafeBufferPointer<Element>) {

[atrick]

@swift-ci test

[meg-gupta]

LGTM

[atrick]

@swift-ci smoke test windows