Revert "[temporary] disable spans over inline elements"

This reverts commit e5c7dfc.

Author: glessard

stdlib/public/core/CollectionOfOne.swift

@@ -166,7 +166,9 @@ extension CollectionOfOne {
     @lifetime(borrow self)
     @_alwaysEmitIntoClient
     get {
-      fatalError("Span over CollectionOfOne is not supported yet.")
+      let pointer = unsafe UnsafePointer<Element>(Builtin.addressOfBorrow(self))
+      let span = unsafe Span(_unsafeStart: pointer, count: 1)
+      return unsafe _overrideLifetime(span, borrowing: self)
     }
   }
 }

stdlib/public/core/InlineArray.swift

@@ -468,7 +468,9 @@ extension InlineArray where Element: ~Copyable {
     @lifetime(borrow self)
     @_alwaysEmitIntoClient
     borrowing get {
-      fatalError("Span over InlineArray is not supported yet.")
+      let pointer = _address
+      let span = unsafe Span(_unsafeStart: pointer, count: count)
+      return unsafe _overrideLifetime(span, borrowing: self)
     }
   }
 }