Update BEP docs to explain NamedSetOfFiles consumption; add example.
Update BEP docs to explain NamedSetOfFiles consumption; add example.

The NamedSetOfFiles event in BEP is tricky to consume due to its recursive,
shared structure and its ordering properties within the BEP stream. Consuming
these events is a common use case as it is necessary to obtain the output files
from a build. This change adds documentation specific to consuming these events
and provides sample pseudocode to that effect.

PiperOrigin-RevId: 363782854

bazelbuild/bazel,cushon/bazel,cushon/bazel,ButterflyNetwork/bazel,katre/bazel,bazelbuild/bazel,cushon/bazel,perezd/bazel,twitter-forks/bazel,ButterflyNetwork/bazel,perezd/bazel,perezd/bazel,ButterflyNetwork/bazel,twitter-forks/bazel,ButterflyNetwork/bazel,perezd/bazel,katre/bazel,cushon/bazel,meteorcloudy/bazel,twitter-forks/bazel,twitter-forks/bazel,meteorcloudy/bazel,perezd/bazel,katre/bazel,perezd/bazel,katre/bazel,ButterflyNetwork/bazel,bazelbuild/bazel,perezd/bazel,meteorcloudy/bazel,meteorcloudy/bazel,meteorcloudy/bazel,cushon/bazel,cushon/bazel,bazelbuild/bazel,katre/bazel,meteorcloudy/bazel,bazelbuild/bazel,twitter-forks/bazel,meteorcloudy/bazel,ButterflyNetwork/bazel,twitter-forks/bazel,bazelbuild/bazel,katre/bazel,twitter-forks/bazel