[Flang] Generate inline reduction loops for elemental count intrinsics (#75774)

This adds a ReductionElementalConversion transform to
OptimizedBufferizationPass, taking hlfir::count(hlfir::elemental) and
generating the inline loop to perform the count of true elements. This
lets us generate a single loop instead of ending up as two plus a
temporary.

Any and All should be able to share the same code with a different
function/initial value.