Fix up sequences that lost inference

Author: natecook1000

stdlib/private/SwiftReflectionTest/SwiftReflectionTest.swift

@@ -226,6 +226,8 @@ internal struct Section {
 
 /// Holds the addresses and sizes of sections related to reflection.
 internal struct ReflectionInfo : Sequence {
+  internal typealias Element = Section?
+  
   /// The name of the loaded image.
   internal let imageName: String
 

stdlib/public/RuntimeModule/Elf.swift

@@ -1266,6 +1266,8 @@ final class ElfImage<SomeElfTraits: ElfTraits>
   }
 
   struct Notes: Sequence {
+    typealias Element = Note
+    
     var image: ElfImage<Traits>
 
     struct NoteIterator: IteratorProtocol {

stdlib/public/RuntimeModule/FramePointerUnwinder.swift

@@ -21,6 +21,7 @@ public struct FramePointerUnwinder<C: Context, M: MemoryReader>: Sequence, Itera
   public typealias Context = C
   public typealias MemoryReader = M
   public typealias Address = Context.Address
+  public typealias Element = RichFrame<Address>
 
   var pc: Address
   var fp: Address