Ecma262: convert some Number:: AOs to use algorithm steps

[michaelficarra]

In the same way we recently rewrote all of the Math built-ins to use algorithm steps (#2122), some of the Number:: AOs can be rewritten in the more typical form, as a sequence of algorithm steps. I've identified the following AOs:

• Number::exponentiate
• Number::multiply
• Number::divide
• Number::remainder
• Number::add

/cc @ryanjduffy in case he has any interest doing another one of these.

[ryanjduffy]

Sure, I'm game.