Move loopdevice module to dm_rust lib

This is a generic module, not specific to apkdmverity. Will be reused
for unit-testing other dm- devices. Also, setup the test infra for
dm_rust module...

Bug: 250880499
Test: atest libdm_rust.test
Test: atest apkdmverity.test
Change-Id: I32971938908ea8c0213583885403910baac8be10
diff --git a/libs/devicemapper/TEST_MAPPING b/libs/devicemapper/TEST_MAPPING
new file mode 100644
index 0000000..23d10c4
--- /dev/null
+++ b/libs/devicemapper/TEST_MAPPING
@@ -0,0 +1,7 @@
+{
+  "avf-presubmit" : [
+    {
+      "name" : "libdm_rust.test"
+    }
+  ]
+}