Improve conformance test generation for tensor operations

Applies to ARGMAX, MATMUL, CONV2D, CONV3D, DEPTHWISE_CONV2D,
TRANSPOSE_CONV2D, FFT2D and RFFT2D.

Improves the coverage with respect to rank, fp_special tests and
covered types for these operators.

Adds support for stable_random_gen and random_const_inputs

Signed-off-by: Ian Tayler Lessa <ian.taylerlessa@arm.com>
Signed-off-by: Jeremy Johnson <jeremy.johnson@arm.com>
Change-Id: Id2204991ae23fc32b79a69b8eac63c54a63c2af1