Parameters of a lazily parsed function used to be parsed eagerly, and parameter
handling was split between Parser::ParseFunctionLiteral and
ParseEagerFunctionBody, leading to inconsistencies.

After this CL, we preparse (lazy parse) the parameters of lazily parsed
functions.

(For arrow functions, we cannot do that ofc.)

This is needed for later features (PreParser with scope analysis).

-- CL adapted from marja's https://codereview.chromium.org/2411793003/

BUG=

Review-Url: https://codereview.chromium.org/2472063002
Cr-Commit-Position: refs/heads/master@{#40771}