It's currently 120 bytes on x86-64, due to one oversized variant
(`Subtype`). This commit boxes `Subtype`'s contents, reducing the size
of `SubregionOrigin` to 32 bytes.

The change speeds things up by avoiding lots of `memcpy` calls, mostly
relating to `RegionConstraintData::constraints`, which is a `BTreeMap`
with `SubregionOrigin` values.

* Serialize the level to something a little more useful for a failure note
  struct
* Update tests accordingly

Co-Authored-By: Ralf Jung <post@ralfj.de>

Get rid of special const intrinsic query in favour of `const_eval`

r? @eddyb

… r=Mark-Simulacrum

Shrink `SubregionOrigin`.

It's currently 120 bytes on x86-64, due to one oversized variant
(`Subtype`). This commit boxes `Subtype`'s contents, reducing the size
of `SubregionOrigin` to 32 bytes.

The change speeds things up by avoiding lots of `memcpy` calls, mostly
relating to `RegionConstraintData::constraints`, which is a `BTreeMap`
with `SubregionOrigin` values.

…json-level, r=Mark-Simulacrum

Fix failure note `to_str` implementation

Serialize the level to something a little more useful for a failure note struct. This fixes rust-lang#60425.

…bini

avoid duplicate issues for Miri build failures

Currently, when Miri regressed from test-pass to test-fail, we pen an issue -- and then when it regresses further from test-fail to build-fail, we open a *second* issue.

This changes the logic to avoid the redundant second issue for Miri.

r? @pietroalbini @kennytm

Add an example to Pin::as_mut

taiki-e/pin-project#89 (comment)

r? @RalfJung

document Miri error categories

r? @oli-obk

…bini

build-manifest: re-add some comments

rust-lang#64543 also reverted the comments I added. This adds them back.
Includes rust-lang#64543.

r? @pietroalbini