[lldb/Plugin] Add artificial stackframe loading in ScriptedThread

This patch adds the ability for ScriptedThread to load artificial stack
frames. To do so, the interpreter instance can create a list that will
contain the frame index and its pc address.

Then, when the Scripted Process plugin stops, it will refresh its
Scripted Threads state by invalidating their register context and load
to list from the interpreter object and reconstruct each frame.

This patch also removes all of the default implementation for
`get_stackframes` from the derived ScriptedThread classes, and add the
interface code for the Scripted Thread Interface.

rdar://88721095

Differential Revision: https://reviews.llvm.org/D119388

Signed-off-by: Med Ismail Bennani <medismail.bennani@gmail.com>

lldb/examples/python/scripted_process/scripted_process.py

@@ -306,9 +306,9 @@ class ScriptedThread:
                 containing for each entry, the frame index, the canonical
                 frame address, the program counter value for that frame
                 and a symbol context.
-                None if the list is empty.
+                The list can be empty.
         """
-        return 0
+        return self.frames
 
     def get_register_info(self):
         if self.register_info is None: