Rework make_filter interface to accept either size_px or radius and d…

[yaugenst-flex]

…l arguments, import all user-facing functions into the plugins/autograd namespace, and add tests

Closes #1775

[tylerflex]

Thanks @yaugenst . Looks good overall, a few details.
The main thing to discuss is the fact that this breaks backwards compabibility with the size -> size_px change. What are your thoughts on that? is autograd so experimental that we can do this safely?

[yaugenst-flex]

The main thing to discuss is the fact that this breaks backwards compabibility with the size -> size_px change. What are your thoughts on that? is autograd so experimental that we can do this safely?

Yeah this is pretty unfortunate, but size is I think too ambiguous... I think (I hope) it's fine? I'm sure there will be other breaking changes too...

[tylerflex]

Let's change target of this to pre/2.8?

[yaugenst-flex]

Oh yeah was just in the process of doing that :)

[tylerflex]

Looks pretty good.

I'm having trouble visualizing the API / if there are any changes? especially to invdes? does it break backwards compatibility?

I also think it would make some sense to define the default parameters, especially for beta, as constants somewhere so we can tweak them more easily.

Thanks @yaugenst-flex

[yaugenst-flex]

I'm having trouble visualizing the API / if there are any changes? especially to invdes? does it break backwards compatibility?

It doesn't break backwards compatibility, no, only if we decide to get rid of the functional interface altogether.

[tylerflex]

let's leave the functional interface but introduce these new classes and maybe change notebooks to use the classes?

[tylerflex]

@yaugenst-flex just checking, where did we leave off with this PR? are you waiting for my review?

[yaugenst-flex]

I thin it was most of the way there, some unresolved things regarding the class constructors for the filters, but I'll finish it up and you can review again, this should be done for 2.8

[yaugenst-flex]

@momchil-flex this is actually backwards compatible and does not require changes to the notebooks I'll run some to be sure but In principle the notebooks can be updated later -> nope

see flexcompute/tidy3d-notebooks#174