This patch exposes the `TypeSynthetic::SetFrontEndWantsDereference` via
the `type synthetic add` command.
The motivation for this is moving the various STL data-formatters to
Python. Those currently set this flag programmatically so that pointers
and references get formatted using the pointee synthetic provider.
Patch that makes use of this new option is:
https://github.com/llvm/llvm-project/pull/187677
Claude helped with writing the test code. Reviewed and cleaned it up
myself
b8b4804d17