Implement add_soong_namespace and add_soong_config_var_value functions

Bug: 193540681
Test: rbcrun build/make/tests/run.rbc
Change-Id: I129136e83d2d00ef5b64d3aab07b98719198dcfe
diff --git a/tests/run.rbc b/tests/run.rbc
index 4cda180..da88886 100644
--- a/tests/run.rbc
+++ b/tests/run.rbc
@@ -63,3 +63,17 @@
     },
     { k:v for k, v in sorted(config.items()) }
 )
+
+ns = globals["$SOONG_CONFIG_NAMESPACES"]
+assert_eq(
+    {
+        "NS1": {
+            "v1": "abc",
+            "v2": "def"
+        },
+        "NS2": {
+            "v3": "xyz"
+        }
+    },
+    {k:v for k, v in sorted(ns.items()) }
+)