- Declaring a variable called "this" for preparsed functions was unnecessary;
  DeclarationScope ctor already adds the variable.

- "arguments" for preparsed scopes need to be declared after parsing the
  function, like it's done in the parser.

- Now arguments_ can be the dummy variable, so adapted code to it.

- A previous refactoring CL ( https://codereview.chromium.org/2638333002 ) was
  incomplete; it had added ParserBase::ParseFunctionBody but
  PreParser::ParseFunction didn't call it. This CL completes that work. This is
  needed for getting "arguments" declared properly for preparsed functions.

- AllocateVariablesRecursively is already called for preparsed scopes (without
  this CL, that is), and it bails out early. However, before the bailout it used
  to dcheck num_stack_slots_ == 0; that is no longer true since we've done scope
  analysis for preparsed scopes.

- Test fix: we cannot have any lazy inner functions in the test, except the
  topmost lazy inner function. Such functions would also be lazy in the parser
  case, and the parser would just throw away their variables. Then the test
  tries to verify the preparsed data against the scopes without variables and fails.

- Disabled a test w/ a sloppy block function, will get that working again in the
  upcoming CLs.

BUG=v8:5516

Review-Url: https://codereview.chromium.org/2655623005
Cr-Commit-Position: refs/heads/master@{#42685}