[Xamarin.Android.Build.Tasks] Timing.xml & android:exported="true" (#7551)

Context: 1efa0cf

API-33 requires that publicly accessible receivers need to use
[`<receiver android:exported="true"/>`][0]in order to them to work.

The `Timing.xml` overlay did not have this attribute, which prevented
the `mono.android.app.DumpTimingData` receiver from working as
intended on Android 12.

Update `Timing.xml` so that the `DumpTimingData` receiver is
appropriately exported and usable on Android 12.

[0]: https://developer.android.com/guide/topics/manifest/receiver-element#exported

Author: dellis1972

src/Xamarin.Android.Build.Tasks/ManifestOverlays/Timing.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <manifest xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools">
   <application>
-    <receiver android:name="mono.android.app.DumpTimingData" tools:node="replace">
+    <receiver android:name="mono.android.app.DumpTimingData" tools:node="replace" android:exported="true">
         <intent-filter>
           <action android:name="mono.android.app.DUMP_TIMING_DATA"/>
         </intent-filter>