feat(xatu): add lexical scope graph

src/xatu/BUILD

@@ -11,6 +11,7 @@ rust_library(
         "rules/manual_inherit.rs",
         "rules/manual_inherit_from.rs",
         "rules/unquoted_uri.rs",
+        "scope_graph.rs",
         "xatu.rs",
     ],
     deps = [
@@ -26,6 +27,15 @@ rust_test(
     deps = [":xatu_lib"],
 )
 
+rust_test(
+    name = "scope_graph_test",
+    srcs = ["scope_graph_test.rs"],
+    deps = [
+        ":xatu_lib",
+        "//third_party/crates:googletest",
+    ],
+)
+
 rust_test(
     name = "xatu_test",
     srcs = ["xatu_test.rs"],