librustdoc: Make RenderOptions boolean fields into newtypes

[jefftt]

closes #87752

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[rust-log-analyzer]

The job aarch64-gnu-llvm-20-2 failed! Check out the build log: (web) (plain enhanced) (plain)

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    |
note: associated function defined here
   --> src/librustdoc/formats/cache.rs:146:19
    |
146 |     pub(crate) fn new(document_private: DocumentPrivate, document_hidden: DocumentHidden) -> Self {
    |                   ^^^ ---------------------------------  -------------------------------
help: try wrapping the expression in `config::DocumentPrivate`
    |
 75 |     let cache = Cache::new(config::DocumentPrivate(false), false);
    |                            ++++++++++++++++++++++++     +
help: try wrapping the expression in `config::DocumentHidden`
    |
 75 |     let cache = Cache::new(false, config::DocumentHidden(false));
    |                                   +++++++++++++++++++++++     +

For more information about this error, try `rustc --explain E0308`.
[RUSTC-TIMING] rustdoc test:true 12.456
error: could not compile `rustdoc` (lib test) due to 1 previous error

[fmease]

Could you please turn all of them into enum { Yes, No }, that's what's more conventional in this repo (and also what Esteban suggested back then (see the PR linked from the issue)).