add implicit named tuple and keyword argument names

[JeffBezanson]

This implements #29333.

I went ahead and added dot syntax as well, i.e. a.b implies b=a.b.

[ararslan]

Based on the doctest failure, it seems this inadvertently made unprovided required kwargs produce an UndefVarError instead of the expected UndefKeywordError.

[tpapp]

I think the dot syntax part, ie plot(x, y; options.width) being equivalent to plot(x, y; width=options.width), is a bit too much for now. I think would be better to just experiment with the feature as described in #29333 first.

[JeffBezanson]

I understand wanting to be cautious here, but I'm pretty sure languages tend to have either both of these features or neither. Also the a.b case should be less controversial, since b is already implicitly quoted, so there is no worry about e.g. renaming variables changing the meaning of a program.