Add verbose logging for app image startup cache feature

Will be parsed from logcat to test the feature.
Logging is of the form: AppImage:load_startup_cache

Bug: 124437687
Bug: 123524494

Test: adb shell device_config put runtime_native use_app_image_startup_cache true
Test: start app
Test: look at logcat
Test: repeat with false

Change-Id: I130ef9e6e4b8cb03497c25cd0a88727d5e60ffbc
diff --git a/runtime/class_linker.cc b/runtime/class_linker.cc
index 148fdba..65fe4e4 100644
--- a/runtime/class_linker.cc
+++ b/runtime/class_linker.cc
@@ -1709,6 +1709,7 @@
 
   bool update_intern_strings;
   if (load_startup_cache) {
+    VLOG(image) << "AppImage:load_startup_cache";
     // Only add the intern table if we are using the startup cache. Otherwise,
     // UpdateInternStrings adds the strings to the intern table.
     intern_table->AddImageStringsToTable(space, func);