vm: improve performance of vm.runIn*()

Optimize for common cases in vm.runInContext() and
vm.runInThisContext().

PR-URL: https://github.com/nodejs/node/pull/10816


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Brian White <mscdex@mscdex.net>