Add YogaKit Shared and iOS version

Summary:
Using shared code for reuse in other platforms based on iOS native implementation.

Adds YogaKit sample.

Adds YogaKit tests (same as objc).

```
YogaKitTest : 80 ms
Facebook.YogaKit.iOS.Tests.exe : 81 ms
Tests run: 11 Passed: 8 Inconclusive: 0 Failed: 3 Ignored: 1
```

Since we don't have extension properties we need to go with a extension method to get access to the YogaLayout .

I m also not sure this is leak free yet, would love some help with testing and feedback about view/node lifecycle
Closes https://github.com/facebook/yoga/pull/336

Reviewed By: splhack

Differential Revision: D4415027

Pulled By: emilsjolander

fbshipit-source-id: c88328212426c3200e6f0c48cda594cd2c432065

csharp/iOS/Facebook.YogaKit.iOS.Sample/Assets.xcassets/AppIcon.appiconset/Contents.json

@@ -0,0 +1,157 @@
+{
+  "images": [
+    {
+      "idiom": "iphone",
+      "size": "29x29",
+      "scale": "1x"
+    },
+    {
+      "idiom": "iphone",
+      "size": "29x29",
+      "scale": "2x"
+    },
+    {
+      "idiom": "iphone",
+      "size": "29x29",
+      "scale": "3x"
+    },
+    {
+      "idiom": "iphone",
+      "size": "40x40",
+      "scale": "2x"
+    },
+    {
+      "idiom": "iphone",
+      "size": "40x40",
+      "scale": "3x"
+    },
+    {
+      "idiom": "iphone",
+      "size": "57x57",
+      "scale": "1x"
+    },
+    {
+      "idiom": "iphone",
+      "size": "57x57",
+      "scale": "2x"
+    },
+    {
+      "idiom": "iphone",
+      "size": "60x60",
+      "scale": "2x"
+    },
+    {
+      "idiom": "iphone",
+      "size": "60x60",
+      "scale": "3x"
+    },
+    {
+      "idiom": "ipad",
+      "size": "29x29",
+      "scale": "1x"
+    },
+    {
+      "idiom": "ipad",
+      "size": "29x29",
+      "scale": "2x"
+    },
+    {
+      "idiom": "ipad",
+      "size": "40x40",
+      "scale": "1x"
+    },
+    {
+      "idiom": "ipad",
+      "size": "40x40",
+      "scale": "2x"
+    },
+    {
+      "idiom": "ipad",
+      "size": "50x50",
+      "scale": "1x"
+    },
+    {
+      "idiom": "ipad",
+      "size": "50x50",
+      "scale": "2x"
+    },
+    {
+      "idiom": "ipad",
+      "size": "72x72",
+      "scale": "1x"
+    },
+    {
+      "idiom": "ipad",
+      "size": "72x72",
+      "scale": "2x"
+    },
+    {
+      "idiom": "ipad",
+      "size": "76x76",
+      "scale": "1x"
+    },
+    {
+      "idiom": "ipad",
+      "size": "76x76",
+      "scale": "2x"
+    },
+    {
+      "size": "24x24",
+      "idiom": "watch",
+      "scale": "2x",
+      "role": "notificationCenter",
+      "subtype": "38mm"
+    },
+    {
+      "size": "27.5x27.5",
+      "idiom": "watch",
+      "scale": "2x",
+      "role": "notificationCenter",
+      "subtype": "42mm"
+    },
+    {
+      "size": "29x29",
+      "idiom": "watch",
+      "role": "companionSettings",
+      "scale": "2x"
+    },
+    {
+      "size": "29x29",
+      "idiom": "watch",
+      "role": "companionSettings",
+      "scale": "3x"
+    },
+    {
+      "size": "40x40",
+      "idiom": "watch",
+      "scale": "2x",
+      "role": "appLauncher",
+      "subtype": "38mm"
+    },
+    {
+      "size": "44x44",
+      "idiom": "watch",
+      "scale": "2x",
+      "role": "longLook",
+      "subtype": "42mm"
+    },
+    {
+      "size": "86x86",
+      "idiom": "watch",
+      "scale": "2x",
+      "role": "quickLook",
+      "subtype": "38mm"
+    },
+    {
+      "size": "98x98",
+      "idiom": "watch",
+      "scale": "2x",
+      "role": "quickLook",
+      "subtype": "42mm"
+    }
+  ],
+  "info": {
+    "version": 1,
+    "author": "xcode"
+  }
+}