by factoring out `fn ctor_fields_span` into a separate function

…y` in a buggy manner

resolve: Print import chains on privacy errors

A part of rust-lang#67951 that doesn't require hacks.
r? @estebank

expand: Implement something similar to `#[cfg(accessible(path))]`

cc rust-lang#64797

The feature is implemented as a `#[cfg_accessible(path)]` attribute macro rather than as `#[cfg(accessible(path))]` because it needs to wait until `path` becomes resolvable, and `cfg` cannot wait, but macros can wait.

Later we can think about desugaring or not desugaring `#[cfg(accessible(path))]` into `#[cfg_accessible(path)]`.

This implementation is also incomplete in the sense that it never returns "false" from `cfg_accessible(path)`, it requires some tweaks to resolve, which is not quite ready to answer queries like this during early resolution.

However, the most important part of this PR is not `cfg_accessible` itself, but expansion infrastructure for retrying expansions.
Before this PR we could say "we cannot resolve this macro path, let's try it later", with this PR we can say "we cannot expand this macro, let's try it later" as well.

This is a pre-requisite for
- turning `#[derive(...)]` into a regular attribute macro,
- properly supporting eager expansion for macros that cannot yet be resolved like
    ```
    fn main() {
        println!(not_available_yet!());
    }

    macro_rules! make_available {
        () => { #[macro_export] macro_rules! not_available_yet { () => { "Hello world!" } }}
    }

    make_available!();
    ```

VariantSizeDifferences: bail on SizeOverflow

Fixes rust-lang#69485.

r? @oli-obk

resolve: Fix regression in resolution of raw keywords in paths

Fixes rust-lang#63882.

Bump the bootstrap compiler

Use sublice patterns to avoid computing the len

r? @Centril

…unimplemented, r=eddyb

Fiddle `ParamEnv` through to a place that used to use `ParamEnv::empty` in a buggy manner

cc rust-lang#69981 (comment)

r? @eddyb