[ASTextNode] Fix text node truncation (#1863)

* Before truncate a text storage in ASTextKitContext reset the text storage to original value

* Fix ASTextNode tests

We should pass in the constrained size in both cases and the sizes should be the same. We adjust the calculated size in ASTextNode to be a bit narrower in the second case if we truncate again with the calculated size as constrained size it will truncate more and the resulting size will shrink.

AsyncDisplayKit/TextKit/ASTextKitContext.h

@@ -10,6 +10,8 @@
 
 #import <UIKit/UIKit.h>
 
+typedef NSTextStorage *(^ASTextKitContextTextStorageCreationBlock)(NSAttributedString *attributedString);
+
 /**
  A threadsafe container for the TextKit components that ASTextKit uses to lay out and truncate its text.
 
@@ -30,10 +32,19 @@
                          constrainedSize:(CGSize)constrainedSize
               layoutManagerCreationBlock:(NSLayoutManager * (^)(void))layoutCreationBlock
                    layoutManagerDelegate:(id<NSLayoutManagerDelegate>)layoutManagerDelegate
-                textStorageCreationBlock:(NSTextStorage * (^)(NSAttributedString *attributedString))textStorageCreationBlock;
+                textStorageCreationBlock:(ASTextKitContextTextStorageCreationBlock)textStorageCreationBlock;
 
+/**
+ Set the constrained size for the text context.
+ */
 @property (nonatomic, assign, readwrite) CGSize constrainedSize;
 
+/**
+ Resets the text storage to the original value in case it was truncated before. This method is called within
+ a locked context.
+ */
+- (void)resetTextStorage;
+
 /**
  All operations on TextKit values MUST occur within this locked context.  Simultaneous access (even non-mutative) to
  TextKit components may cause crashes.