Create canonical flag types for use within Bazel rules.

In an ideal world,  we would use the definitions from skylib. In the real world, we do not want to take a hard dependency on skylib in Bazel, so we will provide a set strictly for built-in Starlark based rules.

Note: These can not be generally used yet. They require --experimental_build_settings_api. That is planned to be turned on in 0.28.

Closes #8639.

PiperOrigin-RevId: 257327261
diff --git a/tools/BUILD b/tools/BUILD
index c13fab2..38689a4 100644
--- a/tools/BUILD
+++ b/tools/BUILD
@@ -13,6 +13,7 @@
         "//tools/buildstamp:srcs",
         "//tools/build_defs:srcs",
         "//tools/build_rules:srcs",
+        "//tools/config:srcs",
         "//tools/coverage:srcs",
         "//tools/java:srcs",
         "//tools/jdk:srcs",