[BOLT] Refactoring of section handling code

Summary:
This is a big refactoring of the section handling code.  I've removed the SectionInfoMap and NoteSectionInfo and stored all the associated info about sections in BinaryContext and BinarySection classes.  BinarySections should now hold all the info we care about for each section.  They can be initialized from SectionRefs but don't necessarily require one to be created.  There are only one or two spots that needed access to the original SectionRef to work properly.

The trickiest part was making sure RewriteInstance.cpp iterated over the proper sets of sections for each of it's different types of processing.  The different sets are broken down roughly as allocatable and non-alloctable and "registered" (I couldn't think up a better name).  "Registered" means that the section has been updated to include output information, i.e. contents, file offset/address, new size, etc.  It may help to have special iterators on BinaryContext to iterate over the different classes to make things easier.  I can do that if you guys think it is worthwhile.

I found pointee_iterator in the llvm ADT code.  Use that for iterating over BBs in BinaryFunction rather than the custom iterator class.

(cherry picked from FBD6879086)