De-pessimize QCryptographicHash::reset() in OpenSSL3 mode

Instead of going through the whole dance with provider loading,
context creation etc, just call EVP_MD_CTX_reset() to reuse the
already-setup context, if any.

This makes QCryptographicHash::reset() adhere to its noexcept
specification again (assuming EVP_MD_CTX_reset() doesn't allocate
state, and, despite its non-void return type, cannot fail on a valid
context), and should greatly improve the speed of reset(), addData(),
resultView() cycles.

Pick-to: 6.5
Change-Id: I7c35b61cbeab1ffd6dd258e8389ea614d49e2e1e
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Jan Grulich <jgrulich@redhat.com>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/corelib/tools/qcryptographichash.cpp

@@ -547,6 +547,12 @@ void QCryptographicHashPrivate::reset() noexcept
         return;
     }
 
+    if (context && !initializationFailed) {
+        // everything already set up - just reset the context
+        EVP_MD_CTX_reset(context.get());
+        return;
+    }
+
     initializationFailed = true;
 
     if (method == QCryptographicHash::Md4) {