Output properties before sets in snapshot module

This ensures a consistent output irrespective of whether property sets
are created before or after the properties are added. This provides a
little more flexibility in the creation code which allows that to be
simplfied.

Also switches from using reflection to a type switch.

Bug: 142918168
Test: m nothing
Change-Id: Ia025bfc751f1217d1658de6fb8e15091ea0ea9ff

sdk/java_sdk_test.go

@@ -920,6 +920,7 @@ java_import {
 module_exports_snapshot {
     name: "myexports@current",
     host_supported: true,
+    java_libs: ["myexports_myjavalib@current"],
     target: {
         android: {
             java_header_libs: ["myexports_androidjavalib@current"],
@@ -928,7 +929,6 @@ module_exports_snapshot {
             java_header_libs: ["myexports_hostjavalib@current"],
         },
     },
-    java_libs: ["myexports_myjavalib@current"],
 }
 `),
 		checkAllCopyRules(`