[lldb] Make use of Scripted{Python,}Interface for ScriptedThreadPlan (#70392)

This patch makes ScriptedThreadPlan conforming to the ScriptedInterface
& ScriptedPythonInterface facilities by introducing 2
ScriptedThreadPlanInterface & ScriptedThreadPlanPythonInterface classes.

This allows us to get rid of every ScriptedThreadPlan-specific SWIG
method and re-use the same affordances as other scripting offordances,
like Scripted{Process,Thread,Platform} & OperatingSystem.

To do so, this adds new transformer methods for `ThreadPlan`, `Stream` &
`Event`, to allow the bijection between C++ objects and their python
counterparts.

Signed-off-by: Med Ismail Bennani <ismail@bennani.ma>