(0.90.10) on_architecture method for all Oceananigans' types

[simone-silvestri]

We have two functions called arch_array and on_architecture that pretty much do the same thing: moving a variable between GPU and CPU. However, neither of them covers all the types in Oceananigans, like Fields or Models.

So, this PR tidies things up a bit. It removes arch_array in favor of on_architecture. In addition, it extends on_architecture to all the types with memory-allocated variables.

[glwagner]

I did not expect to see 88 files changed --- but it indicates the importance of this. Are we also deprecating arch_array? This would break a lot of existing code, but could be a positive change. Or we can deprecate sometime in the future (maybe we can issue a deprecation warning)

[simone-silvestri]

on_architecture for a model seems to be a little complicated because of FFTs that depend on very different plans for GPU and CPU. I am leaning towards leaving on_architecture only for some basics building blocks (fields, grids, some solvers) and not allow on_architecture for models.

[simone-silvestri]

I think we can keep arch_array for some versions but issue a deprecation warning.

[simone-silvestri]

I liked the idea of keeping a list of deprecated functions that will be removed after a couple of releases.
At least users know what has happened and are ready for the change that will happen down the line.
I would go with the majority of the opinions on this one.

[navidcy]

@simone-silvestri when tests pass, is this ready to be merged?

[simone-silvestri]

Should be