Tests for `OffsetArrays-Field` broadcasts

[simone-silvestri]

with @glwagner we introduced broadcasts across fields and OffsetArrays that include halos, so that

field1 = CenterField(grid)
field2 = CenterField(grid)

set!(field1, (x, y, z) -> x)

data = field1.data

field2 .= data

or alternatively

set!(field2, data)

will set not only the interior of the field, but also the halos, without the need of fill_halo_regions!

We need tests to make sure this feature does not break somewhere...

[francispoulin]

Very nice!

[glwagner]

I'm closing this issue because I'm judging that it's not of current, timely relevance to Oceananigans development. If you would like to make it a higher priority or if you think the issue was closed in error please feel free to re-open.