Auto merge of rust-lang#103010 - petrochenkov:effvisdoc, r=GuillaumeGomez

rustdoc: Simplify modifications of effective visibility table

It is now obvious that rustdoc only calls `set_access_level` with foreign def ids and `AccessLevel::Public`.

The second commit makes one more step and separates effective visibilities coming from rustc from similar data collected by rustdoc for extern `DefId`s.
The original table is no longer modified and now only contains local def ids as populated by rustc.

cc rust-lang#102026 `@Bryanskiy`

Author: bors