Start plumbing the type validator logic through to the ValueObjects; allow a ValueObject to have a validator, to update it from the FormatManager, and to retrieve (and cache) the result of the validation

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@217282 91177308-0d34-0410-b5e6-96231b3b80d8