src: improve JS Array creation from C++

src: improve ToV8Value() functions

• Cache the isolate value between calls
• Introduce an overload for dealing with integers/numbers
• Use the vectored v8::Array::New constructor + MaybeStackBuffer for faster array creation

src: simplify JS Array creation

Use ToV8Value() where appropriate to reduce duplication and avoid extra Array::Set() calls.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines