Move the logic for parsing structs and index/field selection expressions from the grammar into TParseContext.

TRAC #22930

Signed-off-by: Nicolas Capens
Signed-off-by: Geoff Lang
Author: Jamie Madill

git-svn-id: https://angleproject.googlecode.com/svn/branches/es3proto@2340 736b8ea6-26fd-11df-bfd4-992fa37f6226