allow init for minkey/maxkey needed by *+Codable.swift.

Author: ehsannas

Firestore/Source/Public/FirebaseFirestore/FIRMaxKey.h

@@ -31,9 +31,6 @@ __attribute__((objc_subclassing_restricted))
 
 /** Returns true if the given object is equal to this, and false otherwise. */
 - (BOOL)isEqual:(nullable id)object;
-
-- (instancetype)init NS_UNAVAILABLE;
-
 @end
 
 NS_ASSUME_NONNULL_END

Firestore/Source/Public/FirebaseFirestore/FIRMinKey.h

@@ -31,9 +31,6 @@ __attribute__((objc_subclassing_restricted))
 
 /** Returns true if the given object is equal to this, and false otherwise. */
 - (BOOL)isEqual:(nullable id)object;
-
-- (instancetype)init NS_UNAVAILABLE;
-
 @end
 
 NS_ASSUME_NONNULL_END

Firestore/Swift/Source/Codable/MaxKey+Codable.swift

@@ -61,5 +61,5 @@ extension CodableMaxKey {
   }
 }
 
-/** Extends RegexValue to conform to Codable. */
+/** Extends MaxKey to conform to Codable. */
 extension FirebaseFirestore.MaxKey: FirebaseFirestore.CodableMaxKey {}

Firestore/Swift/Source/Codable/MinKey+Codable.swift

@@ -61,5 +61,5 @@ extension CodableMinKey {
   }
 }
 
-/** Extends RegexValue to conform to Codable. */
+/** Extends MinKey to conform to Codable. */
 extension FirebaseFirestore.MinKey: FirebaseFirestore.CodableMinKey {}