Add support for elevation prop in Fabric

Summary:
This diff adds support elevation prop in Fabric core, additionally it adds this prop as non collapsable on the view flattening algorithm

changelog: [Internal] internal change in fabric to support elevation prop

Reviewed By: JoshuaGross

Differential Revision: D21896465

fbshipit-source-id: e0854acc0b2ac30eaf3f82d615aab1cf378cc530

ReactCommon/fabric/components/view/ViewProps.cpp

@@ -92,7 +92,9 @@ ViewProps::ViewProps(ViewProps const &sourceProps, RawProps const &rawProps)
           rawProps,
           "collapsable",
           sourceProps.collapsable,
-          true)){};
+          true)),
+      elevation(
+          convertRawProp(rawProps, "elevation", sourceProps.elevation, {})){};
 
 #pragma mark - Convenience Methods
 

ReactCommon/fabric/components/view/ViewProps.h

@@ -59,6 +59,8 @@ class ViewProps : public YogaStylableProps, public AccessibilityProps {
 
   bool collapsable{true};
 
+  int elevation{};
+
 #pragma mark - Convenience Methods
 
   BorderMetrics resolveBorderMetrics(LayoutMetrics const &layoutMetrics) const;

ReactCommon/fabric/components/view/ViewShadowNode.cpp

@@ -43,6 +43,7 @@ void ViewShadowNode::initialize() noexcept {
       viewProps.pointerEvents == PointerEventsMode::None ||
       !viewProps.nativeId.empty() || viewProps.accessible ||
       viewProps.opacity != 1.0 || viewProps.transform != Transform{} ||
+      viewProps.elevation != 0 ||
       (viewProps.zIndex != 0 &&
        viewProps.yogaStyle.positionType() == YGPositionTypeAbsolute) ||
       viewProps.getClipsContentToBounds() ||