This reverts commit 6238e5edbde55fb82982ce4a19a0cbca7fe7eb9d.
We will re-apply this change, but there are some early signs of performance impacts that need to be investigated.
* 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.
The crash happens in the placeholderImage of ASTextNode. The node is not visible in the time it try to get the `placeholderImage` and so the `visibleRange` has count 0 and a crash happens while accessing the first object of an empty array.
* Added a member to `ASTextKitAttributes` that is an optional delegate to the struct's NSLayoutManager.
* Changed ASTextNode to set this delegate to an instance of ASTextNodeWordKerner.
* Updated init method of `ASTextKitContext` to take an optional NSLayoutManager delegate
* Added the files in TextKit folder to the public headers (so we can include ASTextNodeTypes.h)
