Copy --experimental_generated_protos_in_virtual_imports to the host configuration.

That was a rookie mistake.

This allows flipping flag from https://github.com/bazelbuild/bazel/commit/ce65de4ee8e006137c8d927fa474384c0d940cb2.

RELNOTES: None.
PiperOrigin-RevId: 258730568
diff --git a/src/main/java/com/google/devtools/build/lib/rules/proto/ProtoConfiguration.java b/src/main/java/com/google/devtools/build/lib/rules/proto/ProtoConfiguration.java
index fc2ff99..e443051 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/proto/ProtoConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/proto/ProtoConfiguration.java
@@ -217,6 +217,7 @@
       host.ccProtoLibrarySourceSuffixes = ccProtoLibrarySourceSuffixes;
       host.experimentalJavaProtoAddAllowedPublicImports =
           experimentalJavaProtoAddAllowedPublicImports;
+      host.generatedProtosInVirtualImports = generatedProtosInVirtualImports;
       host.doNotUseBuggyImportPath = doNotUseBuggyImportPath;
       return host;
     }