Expose munged visibility attr as a synthetic attr in `bazel query`

Separated out from #23855 to track just the part where we expose munged visibility as a synthetic attr to `bazel query`. This is a FR that can wait, whereas the rest of #23855 is a bug that blocks 8.0.

Start by reading the context in #23855 and the implementation of bazel query, focusing on how visibility is currently represented. Trace the existing munged visibility handling and determine where a synthetic attribute belongs. Done means bazel query exposes that visibility value as a synthetic attribute without taking on the separate blocking bug from #23855.

Written by the indexing model from the issue text.