webnn: Add WPTs for concurrent dispatch() calls
Similar to the existing parallel-compute WPTs, though with more tests
since the TFLite backend has special handling to allow dispatch to be
called on the same MLGraph concurrently
Concurrent calls to compute() and dispatch() are not tested, since the
former will at some point be deprecated for the latter
Bug: 333392274
Change-Id: Iacc48aafc8424cf2042ce467bc39e23d491222df
Cq-Include-Trybots: luci.chromium.try:mac14-blink-rel,mac14.arm64-blink-rel,win11-blink-rel
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5763686
Reviewed-by: Reilly Grant reillyg@chromium.org
Commit-Queue: Austin Sullivan asully@chromium.org
Reviewed-by: Weizhong Xia weizhong@google.com
Cr-Commit-Position: refs/heads/main@{#1340555}