Ed448: check for public key presence on export

Return PUBLIC_KEY_E for wc_ed25519_export_key if public key is not
present.
Return PUBLIC_KEY_E for wc_ed448_export_key if public key is not
present.
Rename several inLen parameters to outLen for consistency.

Fix F-4427

tests/api/test_ed448.c

@@ -500,7 +500,7 @@ int test_wc_Ed448PublicKeyToDer(void)
 
     ExpectIntEQ(wc_ed448_init(&key), 0);
     ExpectIntEQ(wc_Ed448PublicKeyToDer(&key, derBuf, 0, 0),
-        WC_NO_ERR_TRACE(BUFFER_E));
+        WC_NO_ERR_TRACE(PUBLIC_KEY_E));
     wc_ed448_free(&key);
 
     /*  Test good args */