Rollup merge of #68918 - brson:unwrapdoc, r=Dylan-DPC

Rollup merge of #68918 - brson:unwrapdoc, r=Dylan-DPC

Don't use the word "unwrap" to describe "unwrap" methods

It's tautological, and "unwrap" is essentially Rust-specific jargon.

I was teaching a newbie some Rust, and doing the usual hand-waving about error handling using unwrap. They asked what 'unwrap' means. I said look it up in the docs. The docs read (paraphrased) "unwrap unwraps". I was embarrassed.

This changes all the Option/Result functions with unwrapping behavior to use a variation on a single description:

> "Returns the contained `Some/Ok` value [or ...]."

It also renames the closure of `Result::unwrap_or_else` to `default` for consistency with `Option`, and perhaps makes a few other small tweaks.

Previous: https://github.com/rust-lang/rust/pull/68849