Fix a11y update when insert view

[wsdwsd0829]

No description provided.

[Adlai-Holler]

Thanks Max – could you write down the motivation here?

Since not all nodes are backed by _ASDisplayViews (wrapper nodes) should we move this into something like _addSubnode: or a place that is a tighter funnel?

[wsdwsd0829]

As I tested the insertView will be called instead of addSubview below even for the view hierarchy is created first time. Another case is when view tree is updated by removing and inserting a new image node for example, the new image node will not have a11y info without this change.

[Adlai-Holler]

That makes sense but if we put the code in _addSubnode: (not addSubview:) on ASDisplayNode, I think we can cover layer backed nodes and wrapper nodes at the same time. Something along the lines of:

- (void)_addSubnode:(ASDisplayNode *)node {
  // other code
  if (node->_layer) {
    // Find nearest view above (self or parent).
    nearestView.accessibilityElements = nil;`
  }
}

[Adlai-Holler]

Max pointed out to me that the other ASDisplayView subclass methods also follow this pattern, so I think this diff is quite safe.