DEPR: remove NumericIndex.__new__ & ._should_fallback_to_positional
Remove `NumericIndex.__new__` & `._should_fallback_to_positional` to Index. Next up is to actually remove `NumericIndex` from the code base (there is various scaffolding around, that I need to remove/alter at the same time).

This move `NumericIndex._should_fallback_to_positional` to `Index` as-is. There is an issue #51053 that should be fixed, I'll take that in a follow-up so I can get `NumericIndex` removed here, without worrying about that.

xref #42717.
I think the ARM failure is unrelated. Thanks @topper-123 