Fix broken internal anchors in bazel documentation (rules.md)
Fix broken internal anchors in bazel documentation (rules.md)

Links like "#implementation-function" work on the old site (https://docs.bazel.build/versions/main/skylark/rules.html#implementation-function)
but not on the new site which uses underscores instead
(https://bazel.build/rules/rules#implementation_function)

PiperOrigin-RevId: 441547271

katre/bazel,katre/bazel,cushon/bazel,katre/bazel,bazelbuild/bazel,cushon/bazel,katre/bazel,bazelbuild/bazel,bazelbuild/bazel,cushon/bazel,cushon/bazel,bazelbuild/bazel,cushon/bazel,bazelbuild/bazel,bazelbuild/bazel,katre/bazel,katre/bazel,cushon/bazel