src: refactor emit before/after/promiseResolve

Currently EmitBefore, EmitAfter, EmitPromiseResolve are very similar.
This commit suggests extracting the code they have in common to a new
function to reduce code duplication.

PR-URL: https://github.com/nodejs/node/pull/19295


Reviewed-By: Anna Henningsen <anna@addaleax.net>