Rollup merge of #149255 - reddevilmidzy:let-else, r=Kivooeo

Use `let...else` consistently in user-facing diagnostics

resolve: rust-lang/rust#148772

Standardize `let...else` terminology in user-facing diagnostics.

Goal: Consistently use `let...else` in all error/warning messages.

Internal technical names (`let-else`) in comments and documentation remain unchanged.

cc ``@carols10cents,`` ``@jieyouxu``

Author: matthiaskrgr