Rollup merge of #83389 - njasm:test_rustdoc, r=jyn514

add rust-analyzer rustc_private option in librustdoc Cargo.toml

This addition will allow to have code completion while hacking rustdoc with rust-analyzer.

more info: https://rust-analyzer.github.io/manual.html#rust-analyzer.rustcSource

r? `@jyn514`

src/librustdoc/Cargo.toml

@@ -29,3 +29,6 @@ features = ["fmt", "env-filter", "smallvec", "parking_lot", "ansi"]
 
 [dev-dependencies]
 expect-test = "1.0"
+
+[package.metadata.rust-analyzer]
+rustc_private = true