Address feedback.

Author: ehsannas

Firestore/Source/API/FIRBSONBinaryData.mm renamed to Firestore/Source/API/FIRBSONBinaryData.m

@@ -26,12 +26,14 @@ NS_SWIFT_NAME(MaxKey)
 __attribute__((objc_subclassing_restricted))
 @interface FIRMaxKey : NSObject
 
-/** Returns the only instance of MaxKey. */
+/** The shared singleton `MaxKey` instance. */
 @property(class, readonly) FIRMaxKey *shared;
 
 /** 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/API/FIRBSONObjectId.mm renamed to Firestore/Source/API/FIRBSONObjectId.m

@@ -26,12 +26,14 @@ NS_SWIFT_NAME(MinKey)
 __attribute__((objc_subclassing_restricted))
 @interface FIRMinKey : NSObject
 
-/** The only instance of MinKey. */
+/** The shared singleton `MinKey` instance. */
 @property(class, readonly) FIRMinKey *shared;
 
 /** 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