[merp] generate a crash report if process is killed with SIGTERM

See this feature: https://github.com/mono/mono/issues/8236, https://github.com/mono/mono/pull/8240

It seems to have regressed with https://github.com/mono/mono/pull/17310 - we a not getting any information when VSMac hangs (known to be an urgent issue on Catalina) and a user need to force quit. 