[llvm-rc] Serialize HTML resources to .res files (serialization, pt 1).
This allows to process HTML resources defined in .rc scripts and output
them to resulting .res files. Additionally, some infrastructure allowing
to output these files is created.
This is the first resource type we can operate on.
Thanks to Nico Weber for his original work in this area.
Differential Revision: reviews.llvm.org/D37283