The normalize transform should mirror the map transform more closely

The normalizeX and normalizeY transforms mirror mapX and mapY, the only difference being that you specify a shorthand basis instead of a generic map. But the normalize method isn’t a transform, like the map transform: it returns a map implementation. And hence you have to use it in conjunction with the map transform like so:

Plot.map({title: Plot.normalize("first")}, {x: "Date", title: "Close", stroke: "Symbol"})

It would be shorter and more consistent to have normalize be a transform just like map, where you declare outputs and inputs:

Plot.normalize({title: "first"}, {x: "Date", title: "Close", stroke: "Symbol"})

If desired, we could retain the existing normalize method as Plot.normalizer or some such. (We might offer a similar Plot.reducer for reducer implementations in the future.) Possibly we could change Plot.normalize while retaining backwards compatibility by checking what you pass in, but it’s a little dicey. 🙂

Inspired by #1354.

Start by comparing the normalizeX and normalizeY transforms with mapX and mapY, then inspect the normalize method and the transform API. Determine how Plot.normalize should accept declared outputs and inputs, including whether the existing method remains backward-compatible. Done means the proposed transform usage works consistently with map and the relevant existing behavior is covered.