bpo-35568: add 'raise_signal' function (GH-11335)



As in title, expose C `raise` function as `raise_function` in `signal` module. Also drop existing `raise_signal` in `_testcapi` module and replace all usages with new function.


https://bugs.python.org/issue35568
diff --git a/Lib/test/test_regrtest.py b/Lib/test/test_regrtest.py
index a674583..6193776 100644
--- a/Lib/test/test_regrtest.py
+++ b/Lib/test/test_regrtest.py
@@ -26,9 +26,8 @@
 ROOT_DIR = os.path.abspath(os.path.normpath(ROOT_DIR))
 
 TEST_INTERRUPTED = textwrap.dedent("""
-    from signal import SIGINT
+    from signal import SIGINT, raise_signal
     try:
-        from _testcapi import raise_signal
         raise_signal(SIGINT)
     except ImportError:
         import os