Parse a function expression as a primary expression

Parse a function expression as a primary expression
https://bugs.webkit.org/show_bug.cgi?id=140908

Reviewed by Mark Lam.

Moved the code to generate an AST node for a function expression from parseMemberExpression
to parsePrimaryExpression to match the ES6 specification terminology:
https://people.mozilla.org/~jorendorff/es6-draft.html#sec-primary-expression

There should be no behavior change from this change since parsePrimaryExpression is only
called in parseMemberExpression other than the fact failIfStackOverflow() is called.

* parser/Parser.cpp:
(JSC::Parser<LexerType>::parsePrimaryExpression):
(JSC::Parser<LexerType>::parseMemberExpression):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@179159 268f45cc-cd09-0410-ab3c-d52691b4dbfc