ADIOS2: Fix BTD Particle Resize w/ Empty Ranks (#3657)

* ADIOS2: Fix BTD Resize w/ Empty Ranks

For ADIOS2 BP4 and BP5 writes, setting an update of a variable's
(openPMD record's) shape is not sufficient to drop all meta-data
on disk. In situations where the last write to a BTD stage only
adds further particles from a few ranks, we need to pad with
zero-block writes so ADIOS2 `Put` gets called.

Backend details:
- BP4 (as of ADIOS 2.8): last MPI rank's `Put` meta-data wins
- BP5 (as of ADIOS 2.8): everyone has to write an empty block

* [Draft] Start Duplicating All Put Logic

Jeeeeeze.

* Better Work-Around

Compact and general, including MR situations.

0 files changed, 0 insertions, 0 deletions