Support more date formats supported by V8

[gbrail]

A Trireme user found the following Date format that works in V8, but not in Rhino:

$ node

new Date('March 31, 2013 23:59:59.9999')
Sun Mar 31 2013 23:59:59 GMT-0700 (PDT)

$ rhino
Rhino 1.7.6 2015 04 15
js> new Date('March 31, 2013 23:59:59.9999')
Invalid Date

In the interests of V8 compatibility, we should try to figure out what Date format parsing rules they use and implement them.

apigee/trireme#123

[p-bakker]

As Date string parsing through the Date constructor (or Date.parse) is discouraged and the format that V8 seems to parse is not the format that must be parsable according to the EcmaSript spec, if we'd implement this, I think it should be behind the Context.FEATURE_V8_EXTENSIONS flag

[p-bakker]

Probably better to focus on implementing Temporal support in Rhino, instead of trying to implement the same, non-standard behaviour as V8