Add support for getLaunchArgs on Android (#5466)

Add support for getLaunchArgs on Android

**Usage:**

1. **Pass** args in order to run the application on the device using ADB or xcrun or Detox:
    - Detox: `device.launchApp(bundleId,{launchArgs: {'-key1': 'val1'}})` must use launchArgs key, see [docs](https://github.com/wix/Detox/blob/master/docs/APIRef.DeviceObjectAPI.md#7-additional-launch-arguments).
   - ADB: `adb shell am start -n com.yourpackage/com.yourpackage.YourActivity --es launchArgs "{some stringyfied json}"`
   - Xcrun: `/usr/bin/xcrun simctl launch ${udid} ${bundleId} --args -key1 value1 -key2 value2`

2. **Retrieve** the arguments: `const launchArgs = await Navigation.getLaunchArgs();`
   - There is a small difference between platforms on how they pass the launch args:
       - on iOS, the args will be passed as an array of pairs (argv,argc)
       - on Android, the args will be passed in the form of a dictionary

Extract args as a dictionary example:
```javascript
const launchArgs = await Navigation.getLaunchArgs();
let resultArgs = {};
    if (Platform.OS === 'android') {
      resultArgs = launchArgs; // no need to proccess its a dictionary
    } else {
      for (let i = 0; i < launchArgs.length; i += 2) {
        if (i + 1 < launchArgs.length) {
          resultArgs[launchArgs[i]] = launchArgs[i + 1];
        }
      }
    }
```

Author: swabbass

lib/android/app/src/main/java/com/reactnativenavigation/react/NavigationModule.java

@@ -3,6 +3,7 @@
 import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 
+import com.reactnativenavigation.utils.LaunchArgsParser;
 import com.facebook.react.ReactInstanceManager;
 import com.facebook.react.bridge.Arguments;
 import com.facebook.react.bridge.Promise;
@@ -69,6 +70,11 @@ public String getName() {
         return NAME;
     }
 
+    @ReactMethod
+    public void getLaunchArgs(String commandId, Promise promise) {
+        promise.resolve(LaunchArgsParser.parse(activity()));
+    }
+    
     @ReactMethod
     public void getConstants(Promise promise) {
         ReactApplicationContext ctx = getReactApplicationContext();

lib/android/app/src/main/java/com/reactnativenavigation/utils/LaunchArgsParser.java

@@ -0,0 +1,31 @@
+package com.reactnativenavigation.utils;
+
+import android.app.Activity;
+import android.content.Intent;
+import android.os.Bundle;
+
+import com.facebook.react.bridge.Arguments;
+import com.facebook.react.bridge.WritableMap;
+
+public final class LaunchArgsParser {
+
+    private static final String LAUNCH_ARGS = "launchArgs";
+
+    /**
+     * Parses launch args passed to activity intent to WritableMap
+     * @param activity to fetch the extra launch args
+     * @return parsed writable map if it exist, otherwise empty map will be returned
+     */
+    public static WritableMap parse(Activity activity) {
+        if (activity != null) {
+            Intent intent = activity.getIntent();
+            if (intent != null) {
+                Bundle launchArgs = intent.getBundleExtra(LAUNCH_ARGS);
+                if (launchArgs != null) {
+                    return Arguments.fromBundle(launchArgs);
+                }
+            }
+        }
+        return Arguments.createMap();
+    }
+}