Add custom Insights logging for Share Sheet launch, cancel, and post

Summary: Now that FBNativeDialogs is in, extend the Custom Insights logging introduced earlier tonight to Share Sheet operations.

Test Plan: Tested by invoking the share sheet and watching things go.  Hit what I think Jason described as a bug with loginType that's causing the share sheet display to fail, but worked around it for the testing.

Reviewers: jacl, clang

Reviewed By: jacl

CC: msdkexp@

Differential Revision: https://phabricator.fb.com/D583401

src/FBNativeDialogs.m

@@ -87,7 +87,7 @@ + (BOOL)presentShareDialogModallyFrom:(UIViewController*)viewController
 
     [composeViewController setCompletionHandler:^(SLComposeViewControllerResult result) {
         BOOL cancelled = (result == SLComposeViewControllerResultCancelled);
-        NSString *eventToLog = cancelled ? @"_shareSheetCancel" : @"_shareSheetPost";
+        NSString *eventToLog = cancelled ? @"_shareDialogCancel" : @"_shareDialogPost";
         [FBUtility logInsightsEvent:eventToLog session:session];
         if (handler) {
             handler(cancelled ? FBNativeDialogResultCancelled : FBNativeDialogResultSucceeded, nil);
@@ -96,7 +96,7 @@ + (BOOL)presentShareDialogModallyFrom:(UIViewController*)viewController
 
     [viewController presentModalViewController:composeViewController animated:YES];
 
-    [FBUtility logInsightsEvent:@"_shareSheetLaunch" session:session];
+    [FBUtility logInsightsEvent:@"_shareDialogLaunch" session:session];
 
     return YES;
 }