Add feature flag for contact sharing.

SignalServiceKit/src/Messages/Interactions/OWSContact.h

@@ -13,6 +13,8 @@ NS_ASSUME_NONNULL_BEGIN
 @class TSAttachment;
 @class YapDatabaseReadWriteTransaction;
 
+extern BOOL kIsSendingContactSharesEnabled;
+
 typedef NS_ENUM(NSUInteger, OWSContactPhoneType) {
     OWSContactPhoneType_Home = 1,
     OWSContactPhoneType_Mobile,

SignalServiceKit/src/Messages/Interactions/OWSContact.m

@@ -14,6 +14,8 @@
 
 NS_ASSUME_NONNULL_BEGIN
 
+BOOL kIsSendingContactSharesEnabled = YES;
+
 @interface OWSContactPhoneNumber ()
 
 @property (nonatomic) OWSContactPhoneType phoneType;