[X86] combineScalarToVector - handle (v2i64 scalar_to_vector(aextload)) as...

[X86] combineScalarToVector - handle (v2i64 scalar_to_vector(aextload)) as well as (v2i64 scalar_to_vector(aext))

We already fold (v2i64 scalar_to_vector(aext)) -> (v2i64 bitcast(v4i32 scalar_to_vector(x))), this adds support for similar aextload cases and also handles v2f64 cases that wrap the i64 extension behind bitcasts.

Fixes the remaining issue with PR39016