AcceleratedCryptographicHash: Use platform capabilities

Introduce a CNG version for Windows, a CommonCrypto
version for macOS and a GnuTLS version for Linux, as
we're using gnutls _anyway_.

src/linux/acceleratedcryptographichash_gnutls.cpp

@@ -0,0 +1,60 @@
+/*
+ * Use GnuTLS for SHA256
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright (C) 2024 Raspberry Pi Ltd
+ */
+
+#include "acceleratedcryptographichash.h"
+#include "gnutls/crypto.h"
+
+struct AcceleratedCryptographicHash::impl {
+    explicit impl(QCryptographicHash::Algorithm method)
+    {
+        if (method != QCryptographicHash::Sha256)
+            throw std::runtime_error("Only sha256 implemented");
+
+        gnutls_hash_init(&_sha256, GNUTLS_DIG_SHA256);
+
+    }
+
+    ~impl()
+    {
+        gnutls_hash_deinit(_sha256, NULL);
+    }
+
+    void addData(const char *data, int length)
+    {
+        gnutls_hash(_sha256, data, length);
+    }
+
+    void addData(const QByteArray &data)
+    {
+        addData(data.constData(), data.size());
+    }
+
+    QByteArray result()
+    {
+        unsigned char binhash[gnutls_hash_get_len(GNUTLS_DIG_SHA256)];
+        gnutls_hash_output(_sha256, binhash);
+        return QByteArray((char *) binhash, sizeof binhash);
+    }
+
+private:
+    gnutls_hash_hd_t _sha256;
+};
+
+AcceleratedCryptographicHash::AcceleratedCryptographicHash(QCryptographicHash::Algorithm method)
+    : p_Impl(std::make_unique<impl>(method)) {}
+
+AcceleratedCryptographicHash::~AcceleratedCryptographicHash() = default;
+
+void AcceleratedCryptographicHash::addData(const char *data, int length) {
+    p_Impl->addData(data, length);
+}
+void AcceleratedCryptographicHash::addData(const QByteArray &data) {
+    p_Impl->addData(data);
+}
+QByteArray AcceleratedCryptographicHash::result() {
+    return p_Impl->result();
+}