Add --experimental_enable_builtins_injection

Currently a no-op. We will eventually "flip" the flag by removing its default special value, "disabled".

Work toward #11437.

RELNOTES:
PiperOrigin-RevId: 313393458
diff --git a/src/test/java/com/google/devtools/build/lib/packages/StarlarkSemanticsConsistencyTest.java b/src/test/java/com/google/devtools/build/lib/packages/StarlarkSemanticsConsistencyTest.java
index 589d50d..6ae93d9 100644
--- a/src/test/java/com/google/devtools/build/lib/packages/StarlarkSemanticsConsistencyTest.java
+++ b/src/test/java/com/google/devtools/build/lib/packages/StarlarkSemanticsConsistencyTest.java
@@ -124,6 +124,7 @@
         "--experimental_disable_external_package=" + rand.nextBoolean(),
         "--experimental_sibling_repository_layout=" + rand.nextBoolean(),
         "--experimental_allow_incremental_repository_updates=" + rand.nextBoolean(),
+        "--experimental_builtins_bzl_path=" + rand.nextDouble(),
         "--experimental_cc_skylark_api_enabled_packages="
             + rand.nextDouble()
             + ","
@@ -177,6 +178,7 @@
         .experimentalDisableExternalPackage(rand.nextBoolean())
         .experimentalSiblingRepositoryLayout(rand.nextBoolean())
         .experimentalAllowIncrementalRepositoryUpdates(rand.nextBoolean())
+        .experimentalBuiltinsBzlPath(String.valueOf(rand.nextDouble()))
         .experimentalCcStarlarkApiEnabledPackages(
             ImmutableList.of(String.valueOf(rand.nextDouble()), String.valueOf(rand.nextDouble())))
         .experimentalEnableAndroidMigrationApis(rand.nextBoolean())