[QDQ Optimizer] Fix logic that drops Q/DQ ops from QDQ split node groups (#18394)
### Description
- Fix QDQ optimizer logic that drops Q/DQ ops from Split node groups so
that it only occurs when all input/output quantization parameters are
equal.
- Currently, the selector used for this optimization does not ensure
that all quantization parameters are equal.
- Support dropping Q/DQ ops from Split node groups with optional split
inputs (introduced opset 13). This was not working previously.
### Motivation and Context
Fix bugs in handling of QDQ Split node groups.
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Signed-off-by: adrianlizarraga <adlizarraga@microsoft.com>