Fix "since" version for getpid feature.

It was stabilized right before the beta branch was cut for 1.26.0.

See rust-lang#49523 (comment)

This will need to be backported to beta (1.26.0)

Fix "since" version for getpid feature.

It was stabilized right before the beta branch was cut for 1.26.0.

See rust-lang#49523 (comment)

This will need to be backported to beta (1.26.0)

Rollup of 14 pull requests

Successful merges:

 - #49179 (Handle future deprecation annotations )
 - #49512 (Add support for variant and types fields for intra links)
 - #49516 (Add missing anchor for union type fields)
 - #49532 (Add test for rustdoc ignore test)
 - #49533 (Add #[must_use] to a few standard library methods)
 - #49570 (avoid IdxSets containing garbage above the universe length)
 - #49594 (Add some performance guidance to std::fs and std::io docs)
 - #49599 (Fix typo)
 - #49603 (Fix url for intra link provided method)
 - #49609 (run-pass/attr-stmt-expr: expand test cases)
 - #49612 (Fix "since" version for getpid feature.)
 - #49618 (Fix build error when compiling libcore for 16bit targets)
 - #49619 (tweak core::fmt docs)
 - #49623 (update mdbook)

Failed merges:

Fix "since" version for getpid feature.

It was stabilized right before the beta branch was cut for 1.26.0.

See rust-lang#49523 (comment)

This will need to be backported to beta (1.26.0)

Rollup of 25 pull requests

Successful merges:

 - #49179 (Handle future deprecation annotations )
 - #49512 (Add support for variant and types fields for intra links)
 - #49515 (fix targetted value background)
 - #49516 (Add missing anchor for union type fields)
 - #49532 (Add test for rustdoc ignore test)
 - #49533 (Add #[must_use] to a few standard library methods)
 - #49540 (Fix miri Discriminant() for non-ADT)
 - #49559 (Introduce Vec::resize_with method (see #41758))
 - #49570 (avoid IdxSets containing garbage above the universe length)
 - #49577 (Stabilize String::replace_range)
 - #49599 (Fix typo)
 - #49603 (Fix url for intra link provided method)
 - #49607 (Stabilize iterator methods in 1.27)
 - #49609 (run-pass/attr-stmt-expr: expand test cases)
 - #49612 (Fix "since" version for getpid feature.)
 - #49618 (Fix build error when compiling libcore for 16bit targets)
 - #49619 (tweak core::fmt docs)
 - #49637 (Stabilize parent_id())
 - #49639 (Update Cargo)
 - #49628 (Re-write the documentation index)
 - #49594 (Add some performance guidance to std::fs and std::io docs)
 - #49625 (miri: add public alloc_kind accessor)
 - #49634 (Add a test for the fix to issue #43058)
 - #49641 (Regression test for #46314)
 - #49547 (Unignore borrowck test)

Failed merges:

[beta] Update cargo and backport #49612

rust-lang/cargo#5288 fixes a regression
where cargo would update registry on every operation.

Correct a few stability attributes

* `const_indexing` language feature was stabilized in 1.26.0 by #46882
* `Display` impls for `PanicInfo` and `Location` were stabilized in 1.26.0 by #47687
* `TrustedLen` is still unstable so its impls should be as well even though `RangeInclusive` was stabilized by #47813
* `!Send` and `!Sync` for `Args` and `ArgsOs` were stabilized in 1.26.0 by #48005
* `EscapeDefault` has been stable since 1.0.0 so should continue to show that even though it was moved to core in #48735

This could be backported to beta like #49612