ENH: Remove duplicate code in boxlib

[cphyc]

Removes duplication in boxlib frontend.

This is one step aimed at minimizing code duplication.

The duplicates are spotted using

pylint --disable=all --enable=duplicate-code yt/

Note that I have not attempted to fix all duplicate here.

I am not fully satisfied with the way I have de-duplicated code with chombo/boxlib. Any input is welcome!
I'd also be happy to split the PR in multiple chunks.

[neutrinoceros]

Hey, there's a lot going on here, but it sounds like a good idea.
I'd be interested in reviewing specifically the geometry handler dedups, and I'll admit I feel much less confident about deduplicating frontends (and boxlib in particular is a minefield). Maybe you'd like to separate these contributions into different PRs ?

[neutrinoceros]

Looks like you may have prematurely opened this for review, CI is failing.

[matthewturk]

@zingale Can you peek at this real quick? It looks OK to me.

[zingale]

it looks good to me. I haven't explicitly tested it (and don't really work with particles).

[neutrinoceros]

Seems like we haven't been testing Orion2 data with sink files, and this patch broke that (#4078)
I get lost very quickly trying to isolate the part that needs fixing so I'm going to propose a simple revert.

edit: ah, of couse an automatic revert doesn't work because the patch is too big and too old. Welp, looks like we're in for an actual fix then.