[XABT] Move scanning for ACW map JLOs to FindJavaObjectsStep.

[jpobst]

Context: #9893

Building on #9893, this moves the process of scanning for JLOs needed for the ACW map generation task to the FindJavaObjectsStep "linker step".

This process needs interface JLOs, which JavaCallableWrappers doesn't support. Expanding the JCW serialization format to allow interfaces (and other ACW-needed data it didn't already support) resulted in a lot of extra processing and waste.

Instead, we expand the .jlo.xml file to have 2 sections, one for JCW needed data and one for ACW needed data:

<api>
  <jcw-types>
    <type name="MainActivity" package="crc645107ba1b8b6ee4d3" application_java_class="android.app.Application" mono_runtime_initialization="mono.MonoPackageManager.LoadApplication (context);" extends_type="android.app.Activity" partial_assembly_qualified_name="tempbuild.MainActivity, tempbuild">
      <constructors>
        <constructor name="MainActivity" method="n_.ctor:()V:" jni_signature="()V" managed_parameters="" retval="void" is_dynamically_registered="True" />
      </constructors>
      <methods>
        <method name="clone" method="n_clone:()Ljava/lang/Object;:GetCloneHandler" jni_signature="()Ljava/lang/Object;" retval="java.lang.Object" />
        <method name="onCreate" method="n_onCreate:(Landroid/os/Bundle;)V:GetOnCreate_Landroid_os_Bundle_Handler" jni_signature="(Landroid/os/Bundle;)V" params="android.os.Bundle p0" retval="void" super_call="p0" activate_call="p0" />
      </methods>
    </type>
  </jcw-types>
  <acw-types partial-assembly-name="tempbuild" module-name="tempbuild.dll">
    <type assembly-qualified-name="tempbuild.MainActivity, tempbuild, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" compat-jni-name="tempbuild.MainActivity" java-key="crc645107ba1b8b6ee4d3.MainActivity" managed-key="tempbuild.MainActivity" partial-assembly-qualified-name="tempbuild.MainActivity, tempbuild" />
  </acw-types>
</api>

Additionally, for assemblies that cannot contain JLOs that we do not need to scan, we no longer write an "empty" XML file like this: <types was_scanned="False" />. Instead, we now write an actual empty (0 byte) file to disk, which saves build time when deserializing.

Like #9893, this temporarily leaves the old ACW map generation code in place, guarded behind the $(_AndroidJLOCheckedBuild) flag. This flag generates the ACW map both the new and old way, and errors the build if there are differences. (A consistent sort was added so that both maps are sorted the same.)

[jonathanpeppers]

One thing I wondered about this step... If you are building a Release app with 4 RIDs, does this write a copy of the .xml file 4 times? Is there logic that detects the first RID and skips the rest?

The Java objects found are identical between all 4 RIDs. The only thing that would differ, is the BCL sets different trimmer flags based on 32 or 64-bit, different hardware intrinsics, etc. System.Private.CoreLib.dll and a few other System assemblies will differ per RID, but no Android-libraries or user-assemblies would.