COMPMID-424 Add tests for Gaussian3x3

* Add reference implementation and NEON CL validation tests for gaussian3x3
* Add tests for different border modes
* Incoporate PaddingCalculator

Change-Id: Ia3cd5cb2cd0b4d870a217e6aedecc01369dc2541
Reviewed-on: http://mpd-gerrit.cambridge.arm.com/78125
Reviewed-by: Moritz Pflanzer <moritz.pflanzer@arm.com>
Tested-by: Kaizen <jeremy.johnson+kaizengerrit@arm.com>
diff --git a/tests/validation/ReferenceCPP.h b/tests/validation/ReferenceCPP.h
index aeafa76..b6fd901 100644
--- a/tests/validation/ReferenceCPP.h
+++ b/tests/validation/ReferenceCPP.h
@@ -161,6 +161,14 @@
      * @param[in]  shift  Value for down/up conversions.
      */
     static void depth_convert(const RawTensor &src, RawTensor &dst, ConvertPolicy policy, uint32_t shift);
+    /** Function to compute gaussian3x3 filtered result tensor.
+     *
+     * @param[in]  src                   Input tensor.
+     * @param[out] dst                   Result tensor.
+     * @param[in]  border_mode           Border mode
+     * @param[in]  constant_border_value Constant border value if @p border_mode is BorderMode::CONSTANT
+     */
+    static void gaussian3x3(const RawTensor &src, RawTensor &dst, BorderMode border_mode, uint8_t constant_border_value);
     /** Compute GEMM function.
      *
      * @param[in]  src1  First input tensor