Use system separator color in Separator component

[vitalyster]

• border color is too distracting and does not look "native". Now we using system separator color to provide "native" experience :-)

[xmflsct]

Thanks for the PR! Not knowing much about UIColor myself, it seems like it does support dark mode out of the box? If so, shall we apply the same logic to both dark modes of separator as well?

[vitalyster]

Yes, it does. I don't know what two dark variants means there, that is why I did not touch dark modes

[xmflsct]

Cool, in that case we can just apply the same logic to both of the dark modes. :)