COMPMID-424 Add validation tests for Gaussian5x5

* Fix apply_2d_spatial_filter to use double as intermediate type
* Fix tensor_elem_at to use random value if on border and border_mode is
UNDEFINED

Change-Id: I7feea23c4664cc63c5bab936566dc92b98c723b9
Reviewed-on: http://mpd-gerrit.cambridge.arm.com/78905
Tested-by: Kaizen <jeremy.johnson+kaizengerrit@arm.com>
Reviewed-by: Moritz Pflanzer <moritz.pflanzer@arm.com>
11 files changed