[llvm-rc] Add DIALOG(EX) parsing ability (parser, pt 5/8).

This extends the set of resources parsed by llvm-rc by DIALOG and
DIALOGEX.

Additionally, three optional resource statements specific to these two
resources are added: CAPTION, FONT, and STYLE.

Thanks for Nico Weber for his original work in this area.

Differential Revision: https://reviews.llvm.org/D36905

llvm-svn: 312009