…IteratorImpl to avoid exposing default functions outside of the current crate.

Removed unnecessarry empty impls.
Moved code to organise it better

An earlier commit (99ed06e) accidentally changed this paragraph from the
original, imperative "Provide" to the present tense "Provides". The
latter is indeed the standard for Rustdoc comments relating to a
function or method, but this snippet is introducing the Default trait in
general terms and not talking about any particular function. I believe
this change was likely made in error and should be reverted.

…eGomez

Add long error explanation for E0657

Added proper error explanation for issue E0657 in the Rust compiler.

Part of rust-lang#61137

r? @GuillaumeGomez

Hides default fns inside Fuse impl to avoid exposing it to any crate

Fixes rust-lang#70796

@cuviper I've added some default, private traits to do the job for us. If required, I can expose them to a specific visibility if you want to call these functions for rust-lang#70332

r? @cuviper

reword Miri validity errors: undefined -> uninitialized

I don't think we say "undefined value" or anything like that anywhere in the docs or so, but we do use the term "uninitialized memory", so I think we should do the same here.

Longer-term, I think we should also internally rename "undef" to "uninit".

r? @oli-obk

…Simulacrum

Add some regression tests

Closes rust-lang#24843
Closes rust-lang#28575
Closes rust-lang#54067
Closes rust-lang#66868
Closes rust-lang#67893
Closes rust-lang#68813

Miri error messages: avoid try terminology

r? @oli-obk

…ulacrum

Dogfood or_patterns in the standard library

We can start using `or_patterns` in the standard library as a step toward stabilization.

cc rust-lang#54883 @Centril

…vink

Fix typo in Default trait docs: Provides -> Provide

An earlier commit (99ed06e) accidentally changed this paragraph from the original, imperative `Provide` to the present tense `Provides`. The latter is indeed the standard for Rustdoc comments relating to a function or method, but this snippet is introducing the `Default` trait in general terms and not talking about any particular function. I believe this change was likely made in error and should be reverted.