Rollup merge of rust-lang#104359 - Nilstrieb:plus-one, r=fee1-dead

Refactor must_use lint into two parts

Before, the lint did the checking for `must_use` and pretty printing the types in a special format in one pass, causing quite complex and untranslatable code.
Now the collection and printing is split in two. That should also make it easier to translate or extract the type pretty printing in the future.

Also fixes an integer overflow in the array length pluralization
calculation.

fixes rust-lang#104352

Author: Manishearth