`#[coverage(..)]` attribute should apply recursively to nested functions/methods/closures

[Zalathar]

As discussed at the main tracking issue, #84605 (comment), there is a desire for #[coverage(off)] (and #[coverage(on)]) to apply recursively to all functions/methods/closures inside the one being annotated.

The current behaviour is that the attribute only affects the function that it is directly attached to.

@rustbot label +A-code-coverage

[Zalathar]

Previously filed as #93319.