Fix #12656. Make event shorthands an optional module.

Leaving this out saves about 125 bytes gzip. 

This can't be back-ported into 1.9 because we depend on the event name list to do the fixHook patching.

Looking for some advice on a couple of issues. 

First, the unit tests are filled with uses of shorthands so this can't be easily tested. Should I just make a pass through the tests and change them all, then create a small number of shorthand tests? It's a lot of changes, if we do it in the 2.0 branch I think we should do that in 1.9 as well to avoid spurious differences.

Second, what is the best name for this optional module? I named it `event-alias` with a dash to match the file name.