[lldb/Plugins] Improve error reporting with reading memory in Scripted Process

This patch improves the ScriptedPythonInterface::Dispatch method to
support passing lldb_private types to the python implementation.

This will allow, for instance, the Scripted Process python implementation
to report errors when reading memory back to lldb.

To do so, the Dispatch method will transform the private types in the
parameter pack into `PythonObject`s to be able to pass them down to the
python methods.

Then, if the call succeeded, the transformed arguments will be converted
back to their original type and re-assigned in the parameter pack, to
ensure pointers and references behaviours are preserved.

This patch also updates various scripted process python class and tests
to reflect this change.

rdar://100030995

Differential Revision: https://reviews.llvm.org/D134033

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

lldb/test/API/functionalities/scripted_process/TestScriptedProcess.py

@@ -77,6 +77,12 @@ class ScriptedProcesTestCase(TestBase):
         self.assertEqual(process.GetProcessID(), 666)
         self.assertEqual(process.GetNumThreads(), 0)
 
+        addr = 0x500000000
+        buff = process.ReadMemory(addr, 4, error)
+        self.assertEqual(buff, None)
+        self.assertTrue(error.Fail())
+        self.assertEqual(error.GetCString(), "This is an invalid scripted process!")
+
         with open(log_file, 'r') as f:
             log = f.read()
 
@@ -109,9 +115,14 @@ class ScriptedProcesTestCase(TestBase):
         process = target.Launch(launch_info, error)
         self.assertTrue(process and process.IsValid(), PROCESS_IS_VALID)
         self.assertEqual(process.GetProcessID(), 42)
-
         self.assertEqual(process.GetNumThreads(), 1)
 
+        addr = 0x500000000
+        message = "Hello, world!"
+        buff = process.ReadCStringFromMemory(addr, len(message) + 1, error)
+        self.assertSuccess(error)
+        self.assertEqual(buff, message)
+
         thread = process.GetSelectedThread()
         self.assertTrue(thread, "Invalid thread.")
         self.assertEqual(thread.GetThreadID(), 0x19)