Legend rank per pie slice

[my-tien]

This PR makes it possible to pass arrays to the pie property 'legendrank' so that legend rank assignment can be configured per slice.

Changes:

Previously, traces.pie.legendrank only accepted one value that applied for all slices. With this PR, slice legend entries can be individually ranked in the legend. E.g. the below JSON would produce the displayed chart:

{
  "data": [
    {
      "type": "pie",
      "values": [1, 2, 3, 4, 5],
      "labels": ["E", "D", "C", "B", "A"],
      "legendrank": [5, 4, 3, 2, 1]
    }
  ],
  "layout": {
    "width": 500,
    "height": 400,
    "legend": {
      "title": {
        "text": "A legend"
      }
    }
  }
}

Note:

This feature is not expected to work when pie values are not set.

Disclaimer

I am required to add that…

the software is provided "as is", without warranty of any kind, express or implied, including but not limited to the warranties of merchantability, fitness for a particular purpose and noninfringement. in no event shall the authors or copyright holders be liable for any claim, damages or other liability, whether in an action of contract, tort or otherwise, arising from, out of or in connection with the software or the use or other dealings in the software.

[my-tien]

Hi guys, I'm not sure if the failed baselines-b64 test is related to my changes. It seems that the legendrank array doesn't take effect there?

Expected output (and actual output for the baseline test):

output for baselines-b64 test (note incorrect legend entry order):