Support a `macro` without a `doc` value but with `inherit_attrs` referring to another `macro` or `rule` inherit that `doc`

As seen via https://github.com/bazelbuild/stardoc/pull/287, should the lack of a `doc` value to `macro` pick up a value via `inherit_attrs` just like the `attr` values are picked up/merged? i.e. - the lack of a `doc` value, but presents of an `inherit_attrs` also allow the general `docs` to be inherrited?

Review PR #287 and trace the existing handling of macro inherit_attrs for attr and doc values. Confirm the intended behavior for a macro without its own doc value when inherit_attrs points to another macro or rule, and verify that the generated documentation contains the inherited general docs.

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