Overload to `rerender` to keep existing Input values when not provided

[timdeschryver]

This is coming from #365 (comment)

It raises the question if rerender needs to clear the values of input properties that are not provided.
I think it should (similar APIs with other Testing Libraries), but based on the comments I think it would be nice to have an overload to alter this behavior. While helps with the transition to the new version, I think it also helps to improve the DX.