`while_let_loop` suggestions should be auto-fixable

[dswij]

Description

Currently, while_let_loop suggestions can't be applied automatically, and the lint applicability is marked as HasPlaceholder.

[bend-n]

the feature used to not have placeholders, but it was removed due to having too many bugs and being difficult to get right, it seems. it would be trivial for the let _ else { break } case but i think it gets somewhat complicated for the if let _ { stuff } else { break } case