DEPR: Remove int64 uint64 float64 index tests
This PR updates various tests that currently use Int64Index/UInt64Index/Float64Index to instead use `Index` with the relevant dtype (parametrized dtypes where relevant). Sections of the tests suite are changed in separate commits, so it will be easier to separate them out, if desired. 

This PR's first 3 commits correspond to #50052, which again build on #49560, which builds on #50195. Those 3 PRs are not part of this PR, but should ideally be treated as precursors for this PR, if possible.
needs rebase Yeah, this builds on top of #49560. If I can get that PR in, I will update this (and proceed with other remaining Int/Uint/Float64Index removal. Superseded by various other PRs.