handle uplo argument for Symmetric

[oxinabox]

Zygote handles the 2 arg function for Symmetric
ChainRules rightnow only handles the 1 arg function

[sethaxen]

Should be easy to transfer from Zygote. Actually, of all of the Symmetric/Hermitian rules in Zygote, are there any that just should not be in ChainRules?

[oxinabox]

Nope, they all should be.
Only thing that should not be really is things that need to call back into AD (so unrestricted higher ordee functions)
We know how to support that but haven't yet.

Also nonholomorphic things

[sethaxen]

Okay, yeah the power series defaults do call pullback internally, so I'll hold off on any transfer for now.

[sethaxen]

I will transfer over the rrules for the constructor though. Would like to do Hermitian at the same time. How in ChainRules should I test an rrule with complex numbers?

[willtebbutt]

Same as you would with real numbers, just replace everything with complex numbers, including the seed. to_vec should just handle it.