Move CompOS to /system_ext

We shouldn't be on /system since we're not generic (yet).

But we are closely coupled to /system (integrated with ART, will be
contributing to the system server classpath.

Prune the artifact path files to only the ones that are still written
to /system while we figure out what to do with them.

While I'm here, fix writing various Rust dylib.so files to /system by
making sure the "vm" binary prefers the rlibs.

Test: Boots, APEXes present
Bug: 186126194
Change-Id: Id84fb7bf0fb4e0fb56e0cb896394c31e5c7b5124
diff --git a/compos/apex/Android.bp b/compos/apex/Android.bp
index 3a9d5f5..36e3c3e 100644
--- a/compos/apex/Android.bp
+++ b/compos/apex/Android.bp
@@ -37,6 +37,8 @@
     updatable: false,
     platform_apis: true,
 
+    system_ext_specific: true,
+
     binaries: [
         // Used in Android
         "compos_key_cmd",