Refactor `get_first_two_components` to `get_next_component`.

Fixes the following behaviour of `parse_prefix`:
 - series of separator bytes in a prefix are correctly parsed as a single separator
 - device namespace prefixes correctly recognize both `\\` and `/` as separators

gsgdt [https://crates.io/crates/gsgdt] is a crate which provides an
interface for stringly typed graphs. It also provides generation of
graphviz dot format from said graph.

closes rust-lang#79667

functions that does allocations

Move intrinsics lowering pass from the optimization phase (where it
would not run if -Zmir-opt-level=0), to the drop lowering phase where it
runs unconditionally.

The implementation of those intrinsics in code generation and
interpreter is unnecessary. Remove it.

make MIR graphviz generation use gsgdt

gsgdt [https://crates.io/crates/gsgdt] is a crate which provides an
interface for stringly typed graphs. It also provides generation of
graphviz dot format from said graph.

This is the first in a series of PRs on moving graphviz code out of rustc into normal crates and then implementating graph diffing on top of these crates.

r? ``@oli-obk``

Refactor and fix `parse_prefix` on Windows

This PR is an extension of rust-lang#78692 as well as a general refactor of `parse_prefix`:

**Fixes**:
There are two errors in the current implementation of `parse_prefix`:

Firstly, in the current implementation only `\` is recognized as a separator character in device namespace prefixes. This behavior is only correct for verbatim paths; `"\\.\C:/foo"` should be parsed as `"C:"` instead of `"C:/foo"`.

Secondly, the current implementation only handles single separator characters. In non-verbatim paths a series of separator characters should be recognized as a single boundary, e.g. the UNC path `"\\localhost\\\\\\C$\foo"` should be parsed as `"\\localhost\\\\\\C$"` and then `UNC(server: "localhost", share: "C$")`, but currently it is not parsed at all, because it starts being parsed as `\\localhost\` and then has an invalid empty share location.

Paths like `"\\.\C:/foo"` and `"\\localhost\\\\\\C$\foo"` are valid on Windows, they are equivalent to just `"C:\foo"`.

**Refactoring**:
All uses of `&[u8]` within `parse_prefix` are extracted to helper functions and`&OsStr` is used instead. This reduces the number of places unsafe is used:
- `get_first_two_components` is adapted to the more general `parse_next_component` and used in more places
- code for parsing drive prefixes is extracted to `parse_drive`

Remove memoization leftovers from constant evaluation machine

Closes rust-lang#79667

…ikomatsakis

Move binder for dyn to each list item

This essentially changes `ty::Binder<&'tcx List<ExistentialTraitRef>>` to `&'tcx List<ty::Binder<ExistentialTraitRef>>`.

This is a first step in moving the `dyn Trait` representation closer to Chalk, which we've talked about in ``@rust-lang/wg-traits.``

r? ``@nikomatsakis``

…on-panic, r=dtolnay

Fix overflow when converting ZST Vec to VecDeque

```rust
let v = vec![(); 100];
let queue = VecDeque::from(v);
println!("{:?}", queue);
```
This code will currently panic with a capacity overflow.
This PR resolves this issue and makes the code run fine.

Resolves rust-lang#78532

…ulacrum

BTreeMap: more expressive local variables in merge

r? ``@Mark-Simulacrum``

…ulacrum

BTreeSet: simplify implementation of pop_first/pop_last

…and stop it interfering in rust-lang#79245.
r? ``@Mark-Simulacrum``

…Mark-Simulacrum

expand-yaml-anchors: Make the output directory separator-insensitive

Fixes rust-lang#75709

Optimization for bool's PartialOrd impl

Fix rust-lang#80034.

…Dylan-DPC

Always run intrinsics lowering pass

Move intrinsics lowering pass from the optimization phase (where it
would not run if -Zmir-opt-level=0), to the drop lowering phase where it
runs unconditionally.

The implementation of those intrinsics in code generation and
interpreter is unnecessary. Remove it.