build: improve `make coverage`

Run cleanup for all relevant subdirectories, and exclude generated
source files (e.g. `out/Release/...`) from coverage reporting.
Also enable running `make cctest` again (It’s unclear to me why this
was disabled, as it does reduce coverage unnecessarily).

PR-URL: https://github.com/nodejs/node/pull/29487


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>