Fixed #48425 : Various functions taking a `TyCtxt` and a `Span` should be taking a `TyCtxtAt`

Hi @oli-obk
I have done some code refactoring to fix #48425, Please let me know if anything else is required on this.

Better docs and associated SUCCESS/FAILURE for process::ExitCode

Follow-up to https://github.com/rust-lang/rust/pull/48497#discussion_r170676525, since that PR was the minimal thing to unblock https://github.com/rust-lang/rust/issues/48453#issuecomment-368155082.

r? @nikomatsakis

Add resource-suffix option for rustdoc

Alternative version of #48442.

cc @onur

r? @QuietMisdreavus

Update env_logger to 0.5.4

It looks like this cuts down on the number of dependencies in env_logger and
notably cuts out a difference between a shared dependency of rls/cargo. My goal
here is to ensure that when we compile the RLS/Cargo on CI we only compile Cargo
once, and this is one step towards that!

It looks like this cuts down on the number of dependencies in env_logger and
notably cuts out a difference between a shared dependency of rls/cargo. My goal
here is to ensure that when we compile the RLS/Cargo on CI we only compile Cargo
once, and this is one step towards that!

Rollup of 14 pull requests

- Successful merges: #48403, #48432, #48546, #48573, #48590, #48657, #48727, #48732, #48753, #48754, #48761, #48474, #48507, #47463
- Failed merges:

Stabilize FusedIterator

FusedIterator is a marker trait that promises that the implementing
iterator continues to return `None` from `.next()` once it has returned
`None` once (and/or `.next_back()`, if implemented).

The effects of FusedIterator are already widely available through
`.fuse()`, but with stable `FusedIterator`, stable Rust users can
implement this trait for their iterators when appropriate.

Closes #35602

Add new warning for CStr::from_ptr

Fixes #48401.

New Cell docs

This fixes https://github.com/rust-lang/rust/issues/44061

Remove seemingly unused sugarise-doc-comments Python script.

This Python script converts documentation comments from the
`#[doc = "..."]` attribute to the `///` syntax. It was added six
years ago, presumably to help with the transition when `///` was
implemented and hasn't really been touched since. I don't think there's
much value in keeping it around at this point.

while let all the things

Remove a couple of `isize` references from hashmap docs

Also fix a spelling mistake.

Remove useless powerpc64 entry from ARCH_TABLE

Hope, I understood the scope of the fix correctly. closes #47737

Refactor contrived match.

Optimize str::repeat

Improves the performance of `str::repeat` by bulk copying. Here is the benchmarks of `"abcde".repeat(n)`:

|`n`|old [ns/iter]|new [ns/iter]|diff [%]|
---|---|---|---
|1|27.205|27.421|+0.794|
|2|27.500|27.516|+0.0581|
|3|27.923|27.648|-0.985|
|4|31.206|30.145|-3.40|
|5|35.144|31.861|-9.34|
|7|43.131|34.621|-19.7|
|10|54.945|36.203|-34.1|
|100|428.31|52.895|-87.7|

Don't recompute SymbolExportLevel for upstream crates.

The data collected in #48373 suggests that we can avoid generating up to 30% of the LLVM definitions by only instantiating function monomorphizations once with a given crate graph. Some more data, collected with a [proof-of-concept implementation](https://github.com/michaelwoerister/rust/commits/share-generics) of re-using monomorphizations, which is less efficient than the MIR-only RLIB approach, suggests that it's still around 25% LLVM definitions that we can save.

So far, this PR only cleans up handling of symbol export status. Too early to review still.

doc: no need for the reference

Also, we are well within line length limit

Add functions for reversing the bit pattern in an integer

I'm reviving PR #32798 now that the LLVM issues have been resolved.

> This adds the bitreverse intrinsic and adds a reverse_bits function to all integer types.

Raw string error note

Fixes #48395.

I think this note should be helpful enough to solve the issue.

Suggest type for overflowing bin/hex-literals

Fixes #48073

For hexadecimal and binary literals, which overflow, it gives an additional note to the warning message, like in this [comment](https://github.com/rust-lang/rust/issues/48073#issuecomment-365370113).

Additionally it will suggest a type (`X < Y`):
- `iX`: if literal fits in `uX` => `uX`, else => `iY`
- `-iX` => `iY`
- `uX` => `uY`

Exceptions: `isize`, `usize`. I don't think you can make a good suggestion here. The programmer has to figure it out on it's own in this case.

r? @oli-obk

Fix spelling s/casted/cast/

r? @GuillaumeGomez

Slight modification to the as_ref example of std::option::Option

A user in a reddit thread was confused by the name of the variable
"num_as_int"; they thought the example was trying to convert the
string "10" as if it were binary 2 by calling str::len(). In reality,
the example is simply demonstrating how to take an immutable reference
to the value of an Option. The confusion comes from the coincidence
that the length of the string "10" is also its binary representation,
and the implication from the variable names that a conversion was
occuring ("num_as_str" to "num_as_int").

This PR changes the example number to 12 instead of 10, and changes
the variable name from "num_as_int" to "num_length" to better
communicate what the example is doing.

The reddit thread:
https://www.reddit.com/r/rust/comments/7zpvev/notyetawesome_rust_what_use_cases_would_you_like/dur39xw/

This Python script converts documentation comments from the
`#[doc = "..."]` attribute to the `///` syntax. It was added six
years ago, presumably to help with the transition when `///` was
implemented and hasn't really been touched since. I don't think there's
much value in keeping it around at this point.

Whitelist rustc dependencies

As per https://internals.rust-lang.org/t/rustc-dependency-policy/6537/8?u=nikomatsakis

cc @alexcrichton @nikomatsakis