PR #3199 broke the Nyx regression tests. The issue is we require the
particle positions to be in [plo, phi). This won't happen if rhi is
exactly equal to phi. The fix is to make sure rhi is always slightly
inside the domain.

EDIT - fixed this in a different way. Now, when applying periodic
boundaries, the particle positions will be set to be strictly less than
rhi.

There was a flaw in amrex::Geometry::computeRoundoffDomain. If probhi is
close to zero, std::nextafter towards negative infinity will be a very
small number (e.g., 1.e-300). So the function will be able to find the
lowest value of roundoff_hi that's outside the domain within a
reasonable number of iterations.

In the new implementation, we use bisection to find the lowest value of
roundoff_lo that's inside the domain and the highest value fo
roundoff_hi that's inside the domain, up to a tolerance.

X-ref:
- #3243
- #3199

## Summary
This reworks previous changes that created the round off domain which
was done to avoid round off errors when locating particles in the
domain, specifically when handling periodic boundaries. This PR changes
how this is done so that the roundoff domain makes as small a change as
possible.

## Additional background
Previous PRs AMReX-Codes#2839 and AMReX-Codes#2950 created a round off domain that has a
slightly smaller extent that the actual domain. Any particles that ended
up outside the round off domain but inside the actual domain were
shifted to be on the boundary of the round off domain. The main purpose
was to handle problems with periodic boundary with mixed precision
(single precision particles and double precision grid). In that case, it
is possible for a particle to have `z < lo` and `z+(hi-lo) > hi`. It is
also possible for a particle to have `z < hi` but `(z-lo)*dzinv > ihi`
putting it in a grid cell beyond the domain. Unfortunately, the roundoff
domains was being set further inside that was needed and would affect
valid particles that would not have those issues. While the problem is
small, the effects can be noticeable when examining simulation
properties, for example charge conservation in WarpX.

This PR changes the roundoff domain so that only problematic particles
are affected. The code now uses `std::nextafter` to find the exact place
where the problems occurs. At the lower end, it ensures that the casted
position will be greater than ProbLo. At the upper end, it ensures that
`(z-lo)*dzinv <= ihi`.

One comment is that this assumes that particle grid coordinates will
always be calculated at the higher precision, with expressions like `iz
= (int)(z - lo)`, without `lo` being cast to `ParticleReal`.

Co-authored-by: atmyers <[email protected]>

PR AMReX-Codes#3199 broke the Nyx regression tests. The issue is we require the
particle positions to be in [plo, phi). This won't happen if rhi is
exactly equal to phi. The fix is to make sure rhi is always slightly
inside the domain.

EDIT - fixed this in a different way. Now, when applying periodic
boundaries, the particle positions will be set to be strictly less than
rhi.

There was a flaw in amrex::Geometry::computeRoundoffDomain. If probhi is
close to zero, std::nextafter towards negative infinity will be a very
small number (e.g., 1.e-300). So the function will be able to find the
lowest value of roundoff_hi that's outside the domain within a
reasonable number of iterations.

In the new implementation, we use bisection to find the lowest value of
roundoff_lo that's inside the domain and the highest value fo
roundoff_hi that's inside the domain, up to a tolerance.

X-ref:
- AMReX-Codes#3243
- AMReX-Codes#3199

  * Rework handling of roundoff domain extent (AMReX-Codes#3199)

  * Fix periodic boundary bug in AMReX-Codes#3199 (AMReX-Codes#3243)

  * Fix Roundoff Domain (AMReX-Codes#3247)

  * Add Tests/RoundoffDomain (AMReX-Codes#3248)

  * Roundoff errors in computeRoundoffDomain (AMReX-Codes#3255)