Rollup merge of #146150 - weihanglo:rustdoc-emit, r=aDotInTheVoid

fix(rustdoc): match rustc `--emit` precedence

Resolves rust-lang/rust#141664

This changes rustdoc's `--emit` to allow only one instance of each type, regardless of the actual data that `--emit` carries. This matches rustc's `--emit` behavior.

As of the writing, only `dep-info` emit type carries extra data.

Author: Zalathar