Don't show legend for size with scale.zero = true?

Vega-Lite outputs always have zero: true for scale of size to ensure correct scaling.

However, when zero is true, Vega legend always include 0, which looks kinda weird.

For example, in this VG spec from the following VL spec:

{
  "description": "A simple bar chart with embedded data.",
  "data": {
    "values": [
      {"a": "A","b": 10},
      {"a": "B","b": 20},
      {"a": "C","b": 30},
      {"a": "D","b": 40}
    ]
  },
  "mark": "circle",
  "encoding": {
    "x": {"field": "a", "type": "ordinal"},
    "size": {"field": "b", "type": "quantitative", "scale": {"zero": true, "range": [0, 361]}}
  }
}

The field b spans [10,40], but the legend include 0, which is unnecessary.

It’d be great if 0 is excluded.

[jheer]

Right now I’m experimenting with the following and so far it seems to work well: Remove a zero-sized entry if and only if (1) there is an active size encoding driving the legend, (2) the removed value is the first entry in the legend, and (3) the removed value was generated from the scale domain, not supplied as part of an explicit values array. Sound good?

(Note that our legend entry generator has access to the backing scales, but not their Vega specs, so we don’t know if zero: true is set or not.)

[jheer]

Suppression of initial zero-sized legend entries was included in the v3.0.0-beta.15 release.