The default implementations of several `Iterator` methods use `fold` or
`try_fold`, which works, but is overkill for slices and bloats the
amount of LLVM IR generated and consequently hurts compile times.

This commit adds the simple, obvious implementations for `for_each`,
`all`, `any`, `find`, `find_map`, and simplifies the existing
implementations for `position` and `rposition`. These changes reduce
compile times significantly on some benchmarks.

Currently it uses `for x in self`, which seems dubious within an
iterator method. Furthermore, `self.next()` is used in all the other
iterator methods.

PrefixComponent with Prefix::VerbatimDisk does not contain the trailing slash. The documentation here is also inconsistent with the documentation on other variants that reflect the `PrefixComponent::as_os_str()` return value.

…ge of terminology.

Signed-off-by: Rustin-Liu <rustin.liu@gmail.com>

… r=RalfJung

Improve the documentation for ManuallyDrop to resolve conflicting usage of terminology

cc @RalfJung

Follow-up from rust-lang/unsafe-code-guidelines#233

Update transitive dependency to work towards removing syn <1.0 dep

This bumps a couple of transitive dependencies in hopes of eventually not transitively depending on syn <1.0 and friends. The only upstream changes that this is blocked on seems to be mattico/elasticlunr-rs#27 and rust-lang/mdBook#1210.

While working on rust-lang#71875 I noticed we still use syn 0.15 here and there so this is a drive-by PR which aims to help with things a bit.

…methods, r=cuviper

Simpler slice `Iterator` methods

These reduce the amount of LLVM IR generated, helping compile times.

r? @cuviper

Remove `lang_items\(\).*\.unwrap\(\)`

Follows up rust-lang#72170 to remove the remaining uses of `lang_items\(\).*\.unwrap\(\)` (avoids a bunch of potential ICEs when working in `#![no_core]`).

Resolves rust-lang#72195

Updated documentation of Prefix::VerbatimDisk

PrefixComponent with Prefix::VerbatimDisk does not contain the trailing slash. The documentation here is also inconsistent with the documentation on other variants that reflect the `PrefixComponent::as_os_str()` return value.

Implement Default for proc_macro::TokenStream

Hopefully this is uncontroversial. The only reason we've made it this far without is that proc-macro2 snuck this in for their TokenStream.

…lnay

Fix typo Arbintrary to Arbitrary

Signed-off-by: Rustin-Liu <rustin.liu@gmail.com>

Closes rust-lang#72122.