Coverage instruments closure bodies in macros (not the macro body)
Fixes: #84884
This solution might be considered a compromise, but I think it is the
better choice.
The results in the `closure.rs` test correctly resolve all test cases
broken as described in #84884.
One test pattern (in both `closure_macro.rs` and
`closure_macro_async.rs`) was also affected, and removes coverage
statistics for the lines inside the closure, because the closure
includes a macro. (The coverage remains at the callsite of the macro, so
we lose some detail, but there isn't a perfect choice with macros.
Often macro implementations are split across the macro and the callsite,
and there doesn't appear to be a single "right choice" for which body
should be covered. For the current implementation, we can't do both.
The callsite is most likely to be the preferred site for coverage.
r? `@tmandry`
cc: `@wesleywiser`
343a094aa1