Fix several build warnings on RN Tester Android (#41660)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/41660

While working on other things, I noticed those warnings firing on console which I'm fixing here.

Changelog:
[Internal] [Changed] - Fix several build warnings on RN Tester Android

Reviewed By: cipolleschi

Differential Revision: D51589072

fbshipit-source-id: 1ddb29afd0d150f1ccbc7a8def9f27ecedb69724

packages/rn-tester/android/app/src/main/java/com/facebook/react/uiapp/RNTesterActivity.kt

@@ -20,12 +20,11 @@ class RNTesterActivity : ReactActivity() {
 
     override fun onCreate(savedInstanceState: Bundle?) {
       // Get remote param before calling super which uses it
-      val bundle = activity.getIntent()?.getExtras()
+      val bundle = activity.intent?.extras
 
       if (bundle != null && bundle.containsKey(PARAM_ROUTE)) {
         val routeUri = "rntester://example/${bundle.getString(PARAM_ROUTE)}Example"
-        initialProps = Bundle()
-        initialProps?.putString("exampleFromAppetizeParams", routeUri)
+        initialProps = Bundle().apply { putString("exampleFromAppetizeParams", routeUri) }
       }
 
       super.onCreate(savedInstanceState)

packages/rn-tester/android/app/src/main/java/com/facebook/react/uiapp/component/MyLegacyViewManager.kt

@@ -35,15 +35,13 @@ internal class MyLegacyViewManager(reactContext: ReactApplicationContext) :
   }
 
   @ReactProp(name = ViewProps.COLOR)
-  fun setColor(view: MyNativeView, color: String) {
-    view.setBackgroundColor(Color.parseColor(color))
+  fun setColor(view: MyNativeView, color: String?) {
+    color?.let { view.setBackgroundColor(Color.parseColor(it)) }
   }
 
   @ReactProp(name = "cornerRadius")
-  fun setCornerRadius(view: MyNativeView, cornerRadius: Float) {
-    if (cornerRadius !== null) {
-      view.setCornerRadius(cornerRadius)
-    }
+  fun setCornerRadius(view: MyNativeView, cornerRadius: Float?) {
+    cornerRadius?.let { view.setCornerRadius(it) }
   }
 
   override fun getExportedViewConstants(): Map<String, Any> = mapOf("PI" to 3.14)

packages/rn-tester/android/app/src/main/java/com/facebook/react/uiapp/component/MyNativeView.kt

@@ -5,6 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+@file:Suppress("DEPRECATION") // As we want to test RCTEventEmitter here
 package com.facebook.react.uiapp.component
 
 import android.graphics.Color