Set up Gradle build for yogacore

Summary:
I put the CMake file in the root directory to avoid moving the actual `yoga/`
dir around, but created a directory for the Android library manifest nonsense
so it works as its own module you can depend on.

Reviewed By: emilsjolander

Differential Revision: D4913601

fbshipit-source-id: 582064264cf0b6b69c03d0e72ed9dd22d217dd16

yogacore/build.gradle

@@ -0,0 +1,17 @@
+apply plugin: 'com.android.library'
+
+android {
+    compileSdkVersion rootProject.compileSdkVersion
+    buildToolsVersion rootProject.buildToolsVersion
+
+    defaultConfig {
+        minSdkVersion rootProject.minSdkVersion
+        targetSdkVersion rootProject.targetSdkVersion
+    }
+
+    externalNativeBuild {
+        cmake {
+            path '../CMakeLists.txt'
+        }
+    }
+}