n-api: Enable scope and ref APIs during exception

N-API is somewhat strict about blocking calls to many APIs while there
is a pending exception. The NAPI_PREAMBLE macro at the beginning of
many API implementations checks for a pending exception. However, a
subset of the APIs (which don't call back into JavaScript) still need
to work while in a pending-exception state. This changes the reference
APIs (equivalent to v8::Persistent) and handle scope APIs so that they
can be used for cleanup up while an exception is pending.

We may decide to similarly enable a few other APIs later, (which would
be a non-breaking change) but we know at least these are needed now
to unblock some specific scenarios.

Fixes: https://github.com/nodejs/abi-stable-node/issues/122
Fixes: https://github.com/nodejs/abi-stable-node/issues/228
PR-URL: https://github.com/nodejs/node/pull/12524


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Gabriel Schulhof <gabriel.schulhof@intel.com>