[java-runtime] Simplify and fix split configs detection (#9378)

We use [`ApplicationInfo.splitSourceDirs`][0] to detect whether the
application uses [split config `.apk` files][1].  Those files are
created by Android when an `.aab` is used to deploy application, e.g.
via the Google Play Store or manually:

	% dotnet new android
	% dotnet build -c Release
	% java -jar /usr/local/share/dotnet/packs/Microsoft.Android.Sdk.Darwin/34.0.94/tools/bundletool.jar \
	  build-apks --bundle bin/Release/net8.0-android/*-Signed.aab \
	  --output=app.apks --connected-device \
	  --aapt2 /usr/local/share/dotnet/packs/Microsoft.Android.Sdk.Darwin/34.0.94/tools/Darwin/aapt2
	# app.apks contains the "split" apk files.
	
	# can manually install app.apks by using `bundletool.jar install-apks`:
	% java -jar /usr/local/share/dotnet/packs/Microsoft.Android.Sdk.Darwin/34.0.94/tools/bundletool.jar \
	  install-apks --apks=app.apks

When they are present, the "base" `.apk` file in
`splits/base-master.apk` doesn't contain any `lib/` directories and
we can simply skip scanning it for those entries, thus saving on
startup time.  (The `splits/base-<ABI>.apk` file contains the native
libraries of interest to us.)

We used to check whether there are more than one entry in
`splitSourceDirs`, which used to be the case, but it seems that
recent Android versions (at least API-33 and newer) can have just a
single entry in the array.  Because of that, we were scanning all the
`.apk` files on those Android versions, wasting time at startup.

Fix the check by probing whether the array exists and contains at
least a single entry.  Additionally, remove API-21 checks, since this
is our lowest supported API level.

[0]: https://developer.android.com/reference/android/content/pm/ApplicationInfo#splitSourceDirs
[1]: https://developer.android.com/guide/app-bundle

src/Xamarin.Android.Build.Tasks/Resources/MonoRuntimeProvider.Bundled.java

@@ -21,15 +21,12 @@ public void attachInfo (android.content.Context context, android.content.pm.Prov
 		// Mono Runtime Initialization {{{
 		android.content.pm.ApplicationInfo applicationInfo = context.getApplicationInfo ();
 		String[] apks = null;
-		if (android.os.Build.VERSION.SDK_INT >= 21) {
-			String[] splitApks = applicationInfo.splitPublicSourceDirs;
-			if (splitApks != null && splitApks.length > 0) {
-				apks = new String[splitApks.length + 1];
-				apks [0] = applicationInfo.sourceDir;
-				System.arraycopy (splitApks, 0, apks, 1, splitApks.length);
-			}
-		}
-		if (apks == null) {
+		String[] splitApks = applicationInfo.splitSourceDirs;
+		if (splitApks != null && splitApks.length > 0) {
+			apks = new String[splitApks.length + 1];
+			apks [0] = applicationInfo.sourceDir;
+			System.arraycopy (splitApks, 0, apks, 1, splitApks.length);
+		} else {
 			apks = new String[] { applicationInfo.sourceDir };
 		}
 		mono.MonoPackageManager.LoadApplication (context, applicationInfo, apks);
@@ -67,4 +64,3 @@ public int update (android.net.Uri uri, android.content.ContentValues values, St
 		throw new RuntimeException ("This operation is not supported.");
 	}
 }
-

src/java-runtime/java/mono/android/MonoPackageManager.java

@@ -58,13 +58,7 @@ public static void LoadApplication (Context context, ApplicationInfo runtimePack
 				// Should the order change here, src/monodroid/jni/SharedConstants.hh must be updated accordingly
 				//
 				String[] appDirs = new String[] {filesDir, cacheDir, dataDir};
-				boolean haveSplitApks = false;
-
-				if (android.os.Build.VERSION.SDK_INT >= 21) {
-					if (runtimePackage.splitSourceDirs != null) {
-						haveSplitApks = runtimePackage.splitSourceDirs.length > 1;
-					}
-				}
+				boolean haveSplitApks = runtimePackage.splitSourceDirs != null && runtimePackage.splitSourceDirs.length > 0;
 
 				//
 				// Preload DSOs libmonodroid.so depends on so that the dynamic