[hexagon][testing] Better pytest ID strings

[cconvey]

• Add utility functions to allow more human-readable pytest test IDs.
  Helpful when ID strings become too large for humans to easily read.

• Update the test_avg_pool2d_slice.py unit test to use this mechanism.

cc @mehrdadh

[cconvey]

CC: @Lunderberg

[cconvey]

Example of the new ID formatting:

======================================================================== test session starts =========================================================================
platform linux -- Python 3.8.0, pytest-7.1.2, pluggy-1.0.0 -- /usr/bin/python3.8
cachedir: .pytest_cache
rootdir: /home/cconvey/r/cconvey/tvm/pytest-ids
collected 14 items                                                                                                                                                   

tests/python/contrib/test_hexagon/topi/test_avg_pool2d_slice.py::TestAvgPool2dSlice::test_avg_pool2d_slice[nhwc-8h2w32c2w-2d-out_shape[1,8,8,32]-kernel[3,3]-stride[1,1]-dil[1,1]-pad[0,0,0,0]-ceil:F-cnt_padded:T-out_layout:nhwc-8h2w32c2w-2d-float16] PASSED

[cconvey]

@jverma-quic : FYI because you authored one of these files.