For functions declared in source code, the .toString() representation
will be an excerpt of the source code.
* For functions declared with the "function" keyword, the excerpt
  starts at the "function" or "async" keyword and ends at the final "}".
  The previous behavior would start the excerpt at the "(" of the
  parameter list, and prepend a canonical `"function " + name` or
  similar, which would discard comments and formatting surrounding the
  function's name. Anonymous functions declared as function expressions
  no longer get the name "anonymous" in their toString representation.
* For methods, the excerpt starts at the "get", "set", "*" (for
  generator methods), or property name, whichever comes first.
  Previously, the toString representation for methods would use a
  canonical prefix before the "(" of the parameter list. Note that any
  "static" keyword is omitted.
* For arrow functions and class declarations, the excerpt is unchanged.

For functions created with the Function, GeneratorFunction, or
AsyncFunction constructors:
* The string separating the parameter text and body text is now
  "\n) {\n", where previously it was "\n/*``*/) {\n" or ") {\n".
* At one point, newline normalization was required by the spec here,
  but that was removed from the spec, and so this CL does not do it.

Included in this CL is a fix for CreateDynamicFunction parsing. ')'
and '`' characters in the parameter string are no longer disallowed,
and Function("a=function(", "}){") is no longer allowed.

BUG=v8:4958, v8:4230

Review-Url: https://codereview.chromium.org/2156303002
Cr-Commit-Position: refs/heads/master@{#43262}