WebNN: Detect and transform QDQ

This detects potential QDQ (Quantize-Dequantize) patterns in the graph
and transform it to suitable form for backend fusion.
For example, here is the original graph:

    ...               ...
      \               /
       DQ(0)         DQ(1)
        \           /
    transpose(0)  transpose(1)
          \      /
           conv2d(center operator)
             \
          transpose(2)
               \
                Q

The TFlite(LiteRT) backend can fuse conv2d with DQ inputs and Q outputs,
so we should swap the position of DQ(Q) and transpose to make it
suitable for backend fusion. Like this:

    ...               ...
      \               /
   transpose(0)     transpose(1)
        \           /
        DQ(0)      DQ(1)
          \      /
           conv2d(center operator)
             \
              Q
               \
            transpose(2)

Bug: 414330683
Change-Id: I09f94483e48b88a9d4ee487b9861dd877103ec02
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6634994
Reviewed-by: ningxin hu <ningxin.hu@intel.com>
Commit-Queue: Jianxiao Lu <jianxiao.lu@intel.com>
Reviewed-by: Phillis Tang <phillis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1484129}