[Xamarin.Android.Build.Tasks] Add directBootAware if needed.

Fixes dotnet#2081

If a user needs to use the `directBootAware` attribute on
an `application`, `activity` or `service` we also need
to include it on the `MonoRuntimeProvider` so that
native libraries can be resolved correctly. Not doing
so results in the following

	java.lang.UnsatisfiedLinkError: No implementation found for void mono.android.Runtime.register

This commit looks to see if any elements in the manifest
contain `directBootAware`. If there are , then we also
include it in the `provider`.

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/ManifestTest.cs

@@ -266,6 +266,8 @@ public void DirectBootAwareAttribute ()
 				Assert.IsNotNull (le, "no activity element found");
 				Assert.IsTrue (doc.XPathSelectElements ("//activity[@android:directBootAware='true']", nsResolver).Any (),
 						   "'activity' element is not generated as expected.");
+				Assert.IsTrue (doc.XPathSelectElements ("//provider[@android:name='mono.MonoRuntimeProvider' and @android:directBootAware='true']", nsResolver).Any (),
+						   "'provider' element is not generated as expected.");
 			}
 		}
 

src/Xamarin.Android.Build.Tasks/Utilities/ManifestDocument.cs

@@ -634,6 +634,7 @@ XElement CreateMonoRuntimeProvider (string name, string processName, int initOrd
 						new XAttribute (androidNs + "name", name),
 						new XAttribute (androidNs + "exported", "false"),
 						new XAttribute (androidNs + "initOrder", initOrder),
+						new XAttribute (androidNs + "directBootAware", DirectBootAware () ? "true" : "false"),
 						processName == null ? null : new XAttribute (androidNs + "process", processName),
 						new XAttribute (androidNs + "authorities", PackageName + "." + name + ".__mono_init__"));
 		}
@@ -658,6 +659,22 @@ public bool ExtractNativeLibraries ()
 			return true;
 		}
 
+				/// <summary>
+		/// Returns the value of //application/@android:directBootAware.
+		/// </summary>
+		public bool DirectBootAware ()
+		{
+			var processAttrName = androidNs.GetName ("directBootAware");
+			foreach (XElement el in app.Elements ()) {
+				var proc = el.Attribute (processAttrName);
+				if (proc != null)
+					return true;
+			}
+
+			// If android:directBootAware is omitted, returns false.
+			return false;
+		}
+
 		XElement ActivityFromTypeDefinition (TypeDefinition type, string name, int targetSdkVersion)
 		{
 			if (name.StartsWith ("_"))