Use the new BoringSSL ERR_ symbol APIs.

Python needs to map OpenSSL error codes like ERR_R_INTERNAL_ERROR into strings
like "INTERNAL_ERROR". OpenSSL lacks an API for this, so CPython instead
maintains its own table.

This table is necessarily sensitive to the OpenSSL version and causes issues for
BoringSSL. Rather than maintain our own copy of this table, BoringSSL has APIs
to do the thing CPython actually wants. This patch switches CPython to use them.
To keep the patch small, it doesn't ifdef the err_codes_to_names, etc., fields,
but they are no longer necessary.

See openssl/openssl#19848 and
https://discuss.python.org/t/error-tables-in-the-ssl-module/25431 for context.

BoringSSL API addition:
https://boringssl.googlesource.com/boringssl/+/dbad745811195c00b729efd0ee0a09b7d9fce1d2

Modules/_ssl.c

@@ -479,10 +479,30 @@ fill_and_set_sslerror(_sslmodulestate *state,
 {
     PyObject *err_value = NULL, *reason_obj = NULL, *lib_obj = NULL;
     PyObject *verify_obj = NULL, *verify_code_obj = NULL;
-    PyObject *init_value, *msg, *key;
+    PyObject *init_value, *msg;
 
     if (errcode != 0) {
+#if defined(OPENSSL_IS_BORINGSSL)
+        const char *lib_str, *reason_str;
+
+        lib_str = ERR_lib_symbol_name(errcode);
+        if (lib_str != NULL) {
+            lib_obj = PyUnicode_FromString(lib_str);
+            if (lib_obj == NULL) {
+                goto fail;
+            }
+        }
+
+        reason_str = ERR_reason_symbol_name(errcode);
+        if (reason_str != NULL) {
+            reason_obj = PyUnicode_FromString(reason_str);
+            if (reason_obj == NULL) {
+                goto fail;
+            }
+        }
+#else
         int lib, reason;
+        PyObject *key;
 
         lib = ERR_GET_LIB(errcode);
         reason = ERR_GET_REASON(errcode);
@@ -502,6 +522,7 @@ fill_and_set_sslerror(_sslmodulestate *state,
         if (lib_obj == NULL && PyErr_Occurred()) {
             goto fail;
         }
+#endif /* OPENSSL_IS_BORINGSSL */
         if (errstr == NULL)
             errstr = ERR_reason_error_string(errcode);
     }
@@ -6291,6 +6312,11 @@ sslmodule_init_constants(PyObject *m)
 static int
 sslmodule_init_errorcodes(PyObject *module)
 {
+#if defined(OPENSSL_IS_BORINGSSL)
+    /* BoringSSL does not use error tables and instead provides the necessary
+       API directly. */
+    return 0;
+#else
     _sslmodulestate *state = get_ssl_state(module);
 
     struct py_ssl_error_code *errcode;
@@ -6339,6 +6365,7 @@ sslmodule_init_errorcodes(PyObject *module)
     }
 
     return 0;
+#endif /* OPENSSL_IS_BORINGSSL */
 }
 
 static void