Force disable symlink optimization for the virt/compos APEX

Previously, since the virt APEX/compos are configured as non-updatable,
the build system enabled the symlink optimization where files are
installed directly to the system partition and the APEX has symlinks to
the files.  However, this forced us to add those files to
PRODUCT_ARTIFACT_PATH_REQUIREMENT_ALLOWED_LIST as we install the APEX
conditionally - because the inclusion of the APEX is done by a product,
not by the core build system.

This change works around the problem by turning the new switch
`future_updatable` on, so that the symlink optimization is forcibly
disabled.

Bug: 207336449
Test: watch TH
Test: run asit/ota/signing
Change-Id: I841b46895df036f278a85dd318f3317a351992c3
diff --git a/apex/Android.bp b/apex/Android.bp
index 9d6cc94..a2f272e 100644
--- a/apex/Android.bp
+++ b/apex/Android.bp
@@ -15,6 +15,7 @@
 
     // TODO(jiyong): make it updatable
     updatable: false,
+    future_updatable: true,
     platform_apis: true,
 
     system_ext_specific: true,