Various syntactic forms now cause functions to have names where they
didn't before. Per the upcoming changes to the toString spec, only
a name that was literally part of a function's expression or declaration
is meant to be reflected in toString. This also happens to be the same
set of names that V8 currently outputs (without the --harmony-function-name
flag).

This required distinguishing anonymous FunctionExpressions from other sorts
of function definitions (like methods and getters/setters) in the AST, parser,
and at runtime.

The patch also takes the opportunity to remove one more argument (and enum)
from FunctionLiteral, as well as adding a special factory method for the
case of a FunctionLiteral representing toplevel or eval'd code.

BUG=v8:4760
LOG=n

Review URL: https://codereview.chromium.org/1712833002

Cr-Commit-Position: refs/heads/master@{#34132}