Support per-process Application class (AM and client side)

Now the <process> tag supports `android:name`, which takes a custom
Application class name. If omitted, the system defaults to the
class set in the <application> tag, or the default class which is
`android.app.Application`.

Bug: 197264681
Test: atest CtsProcessTest
Change-Id: I0650a4a7c75dc37c00875e4f0ac53656f1cbeac9

core/java/android/app/LoadedApk.java

@@ -1352,7 +1352,9 @@ public final class LoadedApk {
 
         Application app = null;
 
-        String appClass = mApplicationInfo.className;
+        final String myProcessName = Process.myProcessName();
+        String appClass = mApplicationInfo.getCustomApplicationClassNameForProcess(
+                myProcessName);
         if (forceDefaultAppClass || (appClass == null)) {
             appClass = "android.app.Application";
         }