Fix behavior of print() in module extensions (#15883)

Previously, messages printed with `print()` didn't have the usual
`DEBUG:` prefix.

Fixes #14526

Closes #15795.

PiperOrigin-RevId: 459052873
Change-Id: I1b75498d448aaae137dd63ea0a418572097bdac2

Co-authored-by: Fabian Meumertzheim <fabian@meumertzhe.im>
Co-authored-by: Chenchu K <ckolli@google.com>

src/main/java/com/google/devtools/build/lib/bazel/bzlmod/SingleExtensionEvalFunction.java

@@ -86,6 +86,7 @@ public void setRepositoryRemoteExecutor(RepositoryRemoteExecutor repositoryRemot
     this.repositoryRemoteExecutor = repositoryRemoteExecutor;
   }
 
+  @Nullable
   @Override
   public SkyValue compute(SkyKey skyKey, Environment env)
       throws SkyFunctionException, InterruptedException {
@@ -161,6 +162,7 @@ public SkyValue compute(SkyKey skyKey, Environment env)
     try (Mutability mu =
         Mutability.create("module extension", usagesValue.getExtensionUniqueName())) {
       StarlarkThread thread = new StarlarkThread(mu, starlarkSemantics);
+      thread.setPrintHandler(Event.makeDebugPrintHandler(env.getListener()));
       ModuleExtensionContext moduleContext =
           createContext(env, usagesValue, starlarkSemantics, extension);
       threadContext.storeInThread(thread);