Add an API on ValueObject to retrieve the desired dynamic/synthetic combination all at once, if available, working somewhat hard to avoid returning an invalid ValueObject in the process

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@219423 91177308-0d34-0410-b5e6-96231b3b80d8
If a ValueObject has a child that vends synthetic children, but only does so to generate a value for itself, that's not a disqualifier from one-line printing. Also, fetch synthetic values if available and requested for children as well while printing them

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@219427 91177308-0d34-0410-b5e6-96231b3b80d8