This verifies the intra-doc links are correct, and hopefully makes
things easier for new contributors.

This fixes rust-lang#111220 by checking the privacy of tuple constructors using `Self`, so the following code now errors

```rust
mod my {
    pub struct Foo(&'static str);
}

impl AsRef<str> for my::Foo {
    fn as_ref(&self) -> &str {
        let Self(s) = self; // previously compiled, now errors correctly
        s
    }
}
```

…atch, r=dtolnay

Remove structural match from `TypeId`

As per rust-lang#99189 (comment).

> Removing the structural equality might make sense, but is a breaking change that'd require a libs-api FCP.

rust-lang#99189 (comment)

> Landing this PR now (well, mainly the "remove structural equality" part) would unblock `const fn` `TypeId::of`, since we only postponed that because we were guaranteeing too much.

See also rust-lang#99189, rust-lang#101698

…truct-field, r=lcnr

fix for `Self` not respecting tuple Ctor privacy

This PR fixes rust-lang#111220 by checking the privacy of tuple constructors using `Self`, so the following code now errors
```rust
mod my {
    pub struct Foo(&'static str);
}

impl AsRef<str> for my::Foo {
    fn as_ref(&self) -> &str {
        let Self(s) = self; // previously compiled, now errors correctly
        s
    }
}
```

[RFC-2011] Expand more expressions

cc rust-lang#44838

Expands `if`, `let`, `match` and also makes `generic_assert_internals` an allowed feature when using `assert!`. `#![feature(generic_assert)]` is still needed to activate everything.

```rust
#![feature(generic_assert)]

fn fun(a: Option<i32>, b: Option<i32>, c: Option<i32>) {
  assert!(
    if a.is_some() { 1 } else { 2 } == 3
      && if let Some(elem) = b { elem == 4 } else { false }
      && match c { Some(_) => true, None => false }
  );
}

fn main() {
  fun(Some(1), None, Some(2));
}

// Assertion failed: assert!(
//   if a.is_some() { 1 } else { 2 } == 3
//     && if let Some(elem) = b { elem == 4 } else { false }
//     && match c { Some(_) => true, None => false }
// );
//
// With captures:
//   a = Some(1)
//   b = None
//   c = Some(2)
```

Remove DesugaringKind::Replace.

A simple boolean flag is enough.

Generate docs for bootstrap itself

This verifies the intra-doc links are correct, and hopefully makes things easier for new contributors.

Note that this will conflict with rust-lang#111955, i'm pretty sure i typo-ed some of the intra-doc links lol

…yUwU

do not prefer substs relate during coherence

r? `@compiler-errors`