Add CKW writing methods for CL unary ops

* Add writing methods for:
  - Assignment.
  - Cast.
  - Unary expression.
* Add corresponding tests.

Partially resolves: COMPMID-6388.
Signed-off-by: Viet-Hoa Do <viet-hoa.do@arm.com>
Change-Id: Ia654173e2e1ee9cddb7819980251e0591934439f
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/10155
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: Gunes Bayir <gunes.bayir@arm.com>
Reviewed-by: Jakub Sujak <jakub.sujak@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
Benchmark: Arm Jenkins <bsgcomp@arm.com>
diff --git a/compute_kernel_writer/include/ckw/types/ConvertPolicy.h b/compute_kernel_writer/include/ckw/types/ConvertPolicy.h
new file mode 100644
index 0000000..43a37ff
--- /dev/null
+++ b/compute_kernel_writer/include/ckw/types/ConvertPolicy.h
@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2023 Arm Limited.
+ *
+ * SPDX-License-Identifier: MIT
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#ifndef CKW_INCLUDE_CKW_TYPES_CONVERTPOLICY_H
+#define CKW_INCLUDE_CKW_TYPES_CONVERTPOLICY_H
+
+#include <cstdint>
+
+namespace ckw
+{
+
+enum class ConvertPolicy : int32_t
+{
+    None     = 0, // No policy specified.
+    Saturate = 1, // Saturated.
+};
+
+} // namespace ckw
+
+#endif // CKW_INCLUDE_CKW_TYPES_CONVERTPOLICY_H