replace `BitAndAssign` example with something more evocative
replace `BitAndAssign` example with something more evocative

This is the augmented-assignment version of PR #35809.

r? @GuillaumeGomez

improved documentation a la PR #35993

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