Implemented materialization and dematerialization
for variables in the new Materializer.  This is
much easier now that the ValueObject API is solid.

I still have to implement reading bytes into a
ValueObject, but committing what I have so far.

This code is not yet used, so there will be fixes
when I switch the expression parser over to use the
new Materializer.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@179416 91177308-0d34-0410-b5e6-96231b3b80d8