Refactor DependencyResolver#dependentNodeMap to take in a set of toolchain labels instead of the entire toolchain context since that's all the dependency resolver really needs. This will help make cquery transitions outputter easier to implement.

PiperOrigin-RevId: 189342812
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/BuildView.java b/src/main/java/com/google/devtools/build/lib/analysis/BuildView.java
index e9657f8..c788f56 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/BuildView.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/BuildView.java
@@ -1052,7 +1052,9 @@
         configurations.getHostConfiguration(),
         /*aspect=*/ null,
         getConfigurableAttributeKeysForTesting(eventHandler, ctgNode),
-        toolchainContext);
+        toolchainContext == null
+            ? ImmutableSet.of()
+            : toolchainContext.getResolvedToolchainLabels());
   }
 
   /**