Attach experimental platform Starlark APIs to --experimental_platforms_api

Technically, this is a breaking change. However, changes being guarded by this flag were already documented as "experimental", and users can use --experimental_platforms_api to temporarily continue using this API, if they so happened to start depending on it.

RELNOTES: A number of platform-related Starlark APIs which were previously marked "experimental" are now disabled by default, and may be enabled via --experimental_platforms_api
PiperOrigin-RevId: 215963147
diff --git a/src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java b/src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java
index 3ce2097..8246bf7 100644
--- a/src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java
+++ b/src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java
@@ -126,6 +126,7 @@
         "--experimental_enable_android_migration_apis=" + rand.nextBoolean(),
         "--experimental_enable_repo_mapping=" + rand.nextBoolean(),
         "--experimental_remap_main_repo=" + rand.nextBoolean(),
+        "--experimental_platforms_api=" + rand.nextBoolean(),
         "--incompatible_bzl_disallow_load_after_statement=" + rand.nextBoolean(),
         "--incompatible_depset_is_not_iterable=" + rand.nextBoolean(),
         "--incompatible_depset_union=" + rand.nextBoolean(),
@@ -168,6 +169,7 @@
         .experimentalEnableAndroidMigrationApis(rand.nextBoolean())
         .experimentalEnableRepoMapping(rand.nextBoolean())
         .experimentalRemapMainRepo(rand.nextBoolean())
+        .experimentalPlatformsApi(rand.nextBoolean())
         .incompatibleBzlDisallowLoadAfterStatement(rand.nextBoolean())
         .incompatibleDepsetIsNotIterable(rand.nextBoolean())
         .incompatibleDepsetUnion(rand.nextBoolean())