Add docs to Skylark performance about len(depset) vs. if depset.
Add docs to Skylark performance about len(depset) vs. if depset.

PiperOrigin-RevId: 174403764

dslomov/bazel,ulfjack/bazel,davidzchen/bazel,dropbox/bazel,dslomov/bazel-windows,katre/bazel,ButterflyNetwork/bazel,werkt/bazel,spxtr/bazel,werkt/bazel,spxtr/bazel,damienmg/bazel,perezd/bazel,spxtr/bazel,meteorcloudy/bazel,meteorcloudy/bazel,dslomov/bazel,damienmg/bazel,safarmer/bazel,dropbox/bazel,dslomov/bazel-windows,werkt/bazel,aehlig/bazel,aehlig/bazel,twitter-forks/bazel,werkt/bazel,davidzchen/bazel,spxtr/bazel,dslomov/bazel-windows,meteorcloudy/bazel,dslomov/bazel,safarmer/bazel,bazelbuild/bazel,davidzchen/bazel,bazelbuild/bazel,ButterflyNetwork/bazel,spxtr/bazel,cushon/bazel,damienmg/bazel,ulfjack/bazel,perezd/bazel,spxtr/bazel,davidzchen/bazel,dslomov/bazel-windows,twitter-forks/bazel,meteorcloudy/bazel,perezd/bazel,dslomov/bazel,dropbox/bazel,safarmer/bazel,aehlig/bazel,aehlig/bazel,perezd/bazel,dslomov/bazel-windows,damienmg/bazel,damienmg/bazel,werkt/bazel,twitter-forks/bazel,akira-baruah/bazel,cushon/bazel,davidzchen/bazel,twitter-forks/bazel,dslomov/bazel-windows,dslomov/bazel,katre/bazel,cushon/bazel,bazelbuild/bazel,cushon/bazel,werkt/bazel,katre/bazel,twitter-forks/bazel,aehlig/bazel,akira-baruah/bazel,akira-baruah/bazel,spxtr/bazel,safarmer/bazel,perezd/bazel,meteorcloudy/bazel,ButterflyNetwork/bazel,twitter-forks/bazel,damienmg/bazel,akira-baruah/bazel,meteorcloudy/bazel,meteorcloudy/bazel,davidzchen/bazel,dropbox/bazel,bazelbuild/bazel,ButterflyNetwork/bazel,perezd/bazel,safarmer/bazel,katre/bazel,ulfjack/bazel,akira-baruah/bazel,katre/bazel,aehlig/bazel,ButterflyNetwork/bazel,ulfjack/bazel,cushon/bazel,cushon/bazel,katre/bazel,bazelbuild/bazel,akira-baruah/bazel,ulfjack/bazel,dslomov/bazel,dropbox/bazel,aehlig/bazel,ulfjack/bazel,dropbox/bazel,bazelbuild/bazel,davidzchen/bazel,dslomov/bazel,safarmer/bazel,perezd/bazel,twitter-forks/bazel,ButterflyNetwork/bazel,damienmg/bazel,ulfjack/bazel