Give compliance a pkgPath

Change the pkgPath of compliance to android/soong/tools/compliance
to distinguish it from the standard library.

Also add a go.mod file so that the Go tools can find the package.

Test: go test ./...
Change-Id: I061be2b91378db6508e9c88be2548648af8be4e7
diff --git a/tools/compliance/Android.bp b/tools/compliance/Android.bp
index 7d0fb90..17ce9d9 100644
--- a/tools/compliance/Android.bp
+++ b/tools/compliance/Android.bp
@@ -113,5 +113,5 @@
         "golang-protobuf-encoding-prototext",
         "license_metadata_proto",
     ],
-    pkgPath: "compliance",
+    pkgPath: "android/soong/tools/compliance",
 }