gh-76785: Show the Traceback for Uncaught Subinterpreter Exceptions (gh-113034)

When an exception is uncaught in Interpreter.exec_sync(), it helps to show that exception's error display if uncaught in the calling interpreter.  We do so here by generating a TracebackException in the subinterpreter and passing it between interpreters using pickle.

Lib/test/test_interpreters/test_api.py

@@ -525,6 +525,54 @@ class TestInterpreterExecSync(TestBase):
         with self.assertRaises(interpreters.ExecFailure):
             interp.exec_sync('raise Exception')
 
+    def test_display_preserved_exception(self):
+        tempdir = self.temp_dir()
+        modfile = self.make_module('spam', tempdir, text="""
+            def ham():
+                raise RuntimeError('uh-oh!')
+
+            def eggs():
+                ham()
+            """)
+        scriptfile = self.make_script('script.py', tempdir, text="""
+            from test.support import interpreters
+
+            def script():
+                import spam
+                spam.eggs()
+
+            interp = interpreters.create()
+            interp.exec_sync(script)
+            """)
+
+        stdout, stderr = self.assert_python_failure(scriptfile)
+        self.maxDiff = None
+        interpmod_line, = (l for l in stderr.splitlines() if ' exec_sync' in l)
+        #      File "{interpreters.__file__}", line 179, in exec_sync
+        self.assertEqual(stderr, dedent(f"""\
+            Traceback (most recent call last):
+              File "{scriptfile}", line 9, in <module>
+                interp.exec_sync(script)
+                ~~~~~~~~~~~~~~~~^^^^^^^^
+              {interpmod_line.strip()}
+                raise ExecFailure(excinfo)
+            test.support.interpreters.ExecFailure: RuntimeError: uh-oh!
+
+            Uncaught in the interpreter:
+
+            Traceback (most recent call last):
+              File "{scriptfile}", line 6, in script
+                spam.eggs()
+                ~~~~~~~~~^^
+              File "{modfile}", line 6, in eggs
+                ham()
+                ~~~^^
+              File "{modfile}", line 3, in ham
+                raise RuntimeError('uh-oh!')
+            RuntimeError: uh-oh!
+            """))
+        self.assertEqual(stdout, '')
+
     def test_in_thread(self):
         interp = interpreters.create()
         script, file = _captured_script('print("it worked!", end="")')