Have an "any" datatype with a property that requires that the any datatype of the input be the same as the any type of the output

Description

We have operators that can accept any input/output datatype, but they require that the input datatype be identical to the output datatype when a choice is made. So, rather than registering each datatype, it would be nice to have an any datatype with property. This property requires that the choice of an input datatype necessarily imposes the output datatype. More precisely, the same datatype! This would simplify operator registration. Let's take the Pad operator, for example, which can support any data type. Therefore, it wouldn't be useful to say that for a float64 input, I need a float64 output, or an int32 input, then an int32 output...

Proposal

Create a datatype like "any_io" (i for input and o for output) for example

Additional context

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