Literal[...] type annotations for named colormaps

[clbarnes]

It would be helpful if named colormaps could be more discoverable/ autocompleted by using ColormapName = Literal["viridis", "viridis_r", ...].
The ColormapLike type union would then include this in the instead of a raw str.
The ColormapName annotation could be generated by a script from the data files to make sure they're in sync. This also be run on CI to reject builds where it's out of sync.

[tlambert03]

I'm definitely open to that. It will be a very long list (particularly if we include all permutations of namespace, non-namespaces, reversed, etc) ... but I'd also like to see how it feels in an IDE.

[clbarnes]

Here's an (untested) script for doing it https://gist.github.com/clbarnes/102bad110cc5a4d5bdeaa864749afe02 , with and without namespaces and _r.

[tlambert03]

closing after our experiment in #106... thanks for trying :)