Rollup merge of #70949 - WaffleLapkin:simlify_vec_macro, r=petrochenkov
Rollup merge of #70949 - WaffleLapkin:simlify_vec_macro, r=petrochenkov

simplify `vec!` macro

Simplify `vec!` macro by replacing 2 following branches:
- `($($x:expr),*) => (...)`
- `($($x:expr,)*) => (...)`
with one:
- `($($x:expr),* $(,)?) => (...)`

This is a minor change, however, this will make the documentation cleaner

graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust