Add fake concrete iterator for InlineArray

Author: natecook1000

stdlib/public/core/BorrowingIteratorProtocol.swift

@@ -159,7 +159,27 @@ extension Span /*: Sequence /* where Element: ~Copyable */ */ {
 
 extension InlineArray: Sequence /* where Element: ~Copyable */ {
   public typealias Element = Element
-  public typealias Iterator = NeverIterator<Element>
+//  public typealias Iterator = NeverIterator<Element>
+  public typealias BorrowingIterator = Span<Element>
+  
+  // This will NOT work once `Element: ~Copyable` is in the works
+  // Problematic because we can only conform to `Sequence` once, so we
+  // need to provide a single iterator type, but it can't handle both
+  // ~Copyable and copyable elements (I think)
+  public struct Iterator: IteratorProtocol {
+    var array: [count of Element]
+    var index: Int = 0
+    
+    public mutating func next() -> Element? {
+      guard index < array.count else { return nil }
+      defer { index &+= 1 }
+      return array[index]
+    }
+  }
+  
+  public func makeIterator() -> Iterator {
+    .init(array: self)
+  }
 
   @_alwaysEmitIntoClient
   @_lifetime(borrow self)