amrex::UtilCreateCleanDirectory That Only Moves

[ax3l]

For a few of our workflows, I would love to have a variant / new version of amrex::UtilCreateCleanDirectory that:

• move the directory out of the way if it exists, but
• does not create a new directory.

This would be useful because keeping an existing directory around (from an older run that had diagnostics) can create confusion if the new run does not create diagnostics. But, at the same time, there are important workflows (automated optimization) where we do not want to create an empty diags/ folder at all (because the it creates both overheads and our runs are sometimes faster than the creation timestamp).

X-ref: ECP-WarpX/impactx#544