onnxruntime

Refine cast optimizer for safety (#15658)

### Description

Cast optimizer may convert a fp16 node to fp32. This used to be safe as
all fp16 kernels has fp32 implementation. As this assumption is no
longer true, we need to check the validity of the operation



### Motivation and Context

Main work here is to introduce an API to check whether a kernel is
registered. Currently we don't have a way to do that without an operator
node. This needs to be augmented. We need to query whether a kernel is
registered by its property only, so that we can judge whether it is safe
to construct a node long before we actually do so.