[stdlib] Make Optional, Array and Dictionary conditionally Equatable.

Author: huonw

stdlib/public/core/Arrays.swift.gyb

@@ -2187,7 +2187,7 @@ extension _ArrayBufferProtocol {
 
 % for (Self, a_Self) in arrayTypes:
 
-extension ${Self} where Element : Equatable {
+extension ${Self} : Equatable where Element : Equatable {
   /// Returns `true` if these arrays contain the same elements.
   @_inlineable
   public static func ==(lhs: ${Self}<Element>, rhs: ${Self}<Element>) -> Bool {

stdlib/public/core/HashedCollections.swift.gyb

@@ -2709,7 +2709,7 @@ extension Dictionary {
   }
 }
 
-extension Dictionary where Value : Equatable {
+extension Dictionary : Equatable where Value : Equatable {
   @_inlineable // FIXME(sil-serialize-all)
   public static func == (lhs: [Key : Value], rhs: [Key : Value]) -> Bool {
     switch (lhs._variantBuffer, rhs._variantBuffer) {

stdlib/public/core/Optional.swift

@@ -313,7 +313,7 @@ func _diagnoseUnexpectedNilOptional(_filenameStart: Builtin.RawPointer,
     line: UInt(_line))
 }
 
-extension Optional where Wrapped : Equatable {
+extension Optional : Equatable where Wrapped : Equatable {
   /// Returns a Boolean value indicating whether two optional instances are
   /// equal.
   ///