webnn: Initialize memory allocated for CoreML and TFLite-based MLBuffers
base::AlignedAlloc and +[MLMultiArray alloc] do not initialize the
memory they allocate so we need to do it ourselves. Adds a new test to
check that the value of a newly created MLBuffer is well-defined.
Fixed: 358409285
Cq-Include-Trybots: luci.chromium.try:win11-blink-rel,mac14-blink-rel
Change-Id: I1a0bdce492108c0ce5f340db627c6fcb20b6f054
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5773800
Auto-Submit: Reilly Grant reillyg@chromium.org
Commit-Queue: Reilly Grant reillyg@chromium.org
Reviewed-by: Austin Sullivan asully@chromium.org
Cr-Commit-Position: refs/heads/main@{#1339893}