webnn: add fp16 conformance tests for activation operations

[chromium-wpt-export-bot]

This CL is to add fp16 conformance tests for clamp, elu, hardSigmoid,
hardSwish, leakyRelu, prelu, relu, sigmoid, softplus, softsign and tanh
operations.

Bug: 345280754
Change-Id: I4452ae766a47a2619d4a6c8391730fda71c5f7fe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6002852
Commit-Queue: Feng Dai <feng.dai@intel.com>
Reviewed-by: Joshua Bell <jsbell@chromium.org>
Reviewed-by: ningxin hu <ningxin.hu@intel.com>
Cr-Commit-Position: refs/heads/main@{#1435849}

[wpt-pr-bot]

The review process for this patch is being conducted in the Chromium project.

[WeizhongX]

63:59.65 INFO queue closed
63:59.70 INFO ::: Ran 1 of expected 10 iterations.
63:59.70 INFO ::: Reached iteration timeout before finishing 2 or more repeat runs.
63:59.70 INFO ::: At least 2 successful repeat runs are required to validate stability.
63:59.70 INFO ::: Running tests in a loop with restarts 10 times : FAIL
63:59.70 INFO :::
63:59.70 WARNING ::: Test verification TIMEOUT
63:59.70 INFO :::
[taskcluster 2025-03-21 05:36:29.936Z] === Task Finished ===
[taskcluster 2025-03-21 05:36:30.338Z] Unsuccessful task run with exit code: 1 completed in 3995.496 seconds

[WeizhongX]

@KyleJu @jcscottiii pls help take a look.

[jonathan-j-lee]

webnn/ generates a lot (hundreds) of tests due to ?(c|g|n)pu parameterization, and I think wpt run is trying to check the flakiness of them all. If so, there's not much we can do about the timeout.

In any case, looks like Firefox fails all the tests anyway due to lack of support. Let's merge @KyleJu @jcscottiii? Thanks!