Android: Accept Throwables in Promise.reject()

Summary:
public

Fixes #4309

This adds the possibility to reject `Promise` instances with `Throwable`s in java, instead of strings.
For now, it only reads the message, but we can add more features on top of this, e.g. forwarding the error stack.

Reviewed By: andreicoman11

Differential Revision: D2708192

fb-gh-sync-id: ca5ff584eca29370a9f9b780fa9825b17863a7e9

ReactAndroid/src/main/java/com/facebook/react/bridge/Promise.java

@@ -18,5 +18,6 @@ package com.facebook.react.bridge;
  */
 public interface Promise {
   void resolve(Object value);
+  void reject(Throwable reason);
   void reject(String reason);
 }

ReactAndroid/src/main/java/com/facebook/react/bridge/PromiseImpl.java

@@ -30,6 +30,11 @@ public class PromiseImpl implements Promise {
     }
   }
 
+  @Override
+  public void reject(Throwable reason) {
+    reject(reason.getMessage());
+  }
+
   @Override
   public void reject(String reason) {
     if (mReject != null) {