Add support for array new

[andykaylor]

Implement handling of the array new operator and any additional details needed to make this work. This will involve array cookie support in CIRGenCXXABI, which in turn will require creating subclasses of CIRGenItaniumCXXABI to get the AppleARM64 ABI right.

[andykaylor]

I'm starting to work on this.

[bcardosolopes]

Awesome!

[ghehg]

Thanks a lot!
Andy, since you are adding array cookie support, I'd like share with you about a very related issue that I just created
#1285
It's about array delete, whose unimplemented lowering may just benefit from what you plan to do.