rollup merge of #18229 : bjz/ttdelim
rollup merge of #18231 : cakebaker/fix_greater_than_forty_two_closure
rollup merge of #18235 : nikomatsakis/issue-18209
rollup merge of #18239 : msiemens/fix-ice-rename-failed
rollup merge of #18244 : areski/pr-fix-string-doc
rollup merge of #18250 : dotdash/fix_aliasing
rollup merge of #18251 : steveklabnik/build_module_guide
rollup merge of #18256 : SimonSapin/view_item_to_string
rollup merge of #18257 : globin/master
rollup merge of #18265 : jakub-/mailmap
rollup merge of #18266 : nick29581/vtable2.rs
rollup merge of #18303 : cgaebel/make-vec-match-slice
return &mut T from the arenas, not &T

The arenas write the value to memory and then return a non-aliasing
reference to it. The returned reference can be mutable and can be
coerced to an immutable one.

[breaking-change]
Untabify rustup.sh
Add @thestinger comment explaining that shrink_to_fit might drop down as close as possible but not to the minimun
rollup merge of #18309 : cakebaker/fix_off_by_one
rollup merge of #18315 : arielb1/constexpr-addr
rollup merge of #18316 : thestinger/raw
rollup merge of #18320 : chastell/guide_simplify_formatting
rollup merge of #18321 : chastell/guide_refresh_testing_output