* Explicit filtering of hydro fluxes and source term. (AMReX-Combustion#112)

This commit implements explicit filtering of the hydro fluxes and
source term (for both MOL and PPM code paths). This is necessary to
perform explicitly filtered Large Eddy Simulations.

Contains:
- regressions tests
- documentation
- CMake implementation

* Remove legacy Fortran code. (AMReX-Combustion#252)

* Use default for trivial constructors and only build HIP in CI for gfx908 (AMReX-Combustion#434)

* Use default for trivial constructors.

* Only build HIP in CI for gfx908.

* Update PelePhysics.

* Fixes to header files (AMReX-Combustion#439)

* Fixes to header files.

* Update PelePhysics submodule.

* More fixes.

* Initialize xdiff in HIT.

* Invert some mfiter loops (AMReX-Combustion#446)

Co-authored-by: Jon Rood <[email protected]>

* Add GPU syncs because MF ParallelFor is non-blocking (AMReX-Combustion#471)

* Rename header guards (AMReX-Combustion#506)

* Replace _OPENMP with AMREX_USE_OMP to support Ascent. (AMReX-Combustion#519)

* Address some warnings (AMReX-Combustion#554)

* remove dependence of Filter on Utilities (#710)

* move files

* docs for filter

* use amrex Pi instead of PeleC Pi

---------

Co-authored-by: Marc T. Henry de Frahan <[email protected]>
Co-authored-by: Jon Rood <[email protected]>