Helps users to understand capacity related values, which may surpise on
Windows.

Also is a step towards clarifying understanding of `OsStr`'s len() return
value.

Rollup of 13 pull requests

Successful merges:

 - #56141 ([std] Osstr len clarity)
 - #56366 (Stabilize self_in_typedefs feature)
 - #56395 (Stabilize dbg!(...))
 - #56401 (Move VecDeque::resize_with out of the impl<T:Clone> block)
 - #56402 (Improve the unstable book example for #[marker] trait)
 - #56412 (Update tracking issue for `extern_crate_self`)
 - #56416 (Remove unneeded body class selector)
 - #56418 (Fix failing tidy (line endings on Windows))
 - #56419 (Remove some uses of try!)
 - #56432 (Update issue number of `shrink_to` methods to point the tracking issue)
 - #56433 (Add description about `crate` for parse_visibility's comment)
 - #56435 (make the C part of compiler-builtins opt-out)
 - #56438 (Remove not used `DotEq` token)

Failed merges:

r? @ghost

…Mark-Simulacrum

Emphasise that an OsStr[ing] is not necessarily a platform string

Fixes rust-lang#53261

Since that issue was filed, rust-lang#56141 added a further clarification to the `OsString` docs. However the ffi docs may still leave the impression that an `OsStr` is in the platform native form. This PR aims to further emphasise that an `OsStr` is not necessarily a platform string.

…Mark-Simulacrum

Emphasise that an OsStr[ing] is not necessarily a platform string

Fixes rust-lang#53261

Since that issue was filed, rust-lang#56141 added a further clarification to the `OsString` docs. However the ffi docs may still leave the impression that an `OsStr` is in the platform native form. This PR aims to further emphasise that an `OsStr` is not necessarily a platform string.

…Mark-Simulacrum

Emphasise that an OsStr[ing] is not necessarily a platform string

Fixes rust-lang#53261

Since that issue was filed, rust-lang#56141 added a further clarification to the `OsString` docs. However the ffi docs may still leave the impression that an `OsStr` is in the platform native form. This PR aims to further emphasise that an `OsStr` is not necessarily a platform string.