feat: add label encoding

[kanitw]

Redo of #7222 so we have a proper review.

To dos:

• [x] use _label as a suffix for examples

• [x] enumerate examples for different mark types:

  • [ ] bar_label (labeling vertical bar chart -- this should be a modification of bar.vl.json to add labels)

    • [ ] auto-rotate for vertical bars

  • [x] bar_horizontal_label (labeling vertical bar chart)

  • [x] bar_negative_label (labeling vertical bar chart -- this should be a modification of bar.vl.json to add labels)

  • [ ] bar_negative_horizontal_label (labeling vertical bar chart)

    • [ ] https://github.com/vega/vega-lite/issues/7881 (Can do after release?)
    • [ ] replace bar_negative_horizontal_label

  • [x] stacked_bar_v_label (labeling vertical bar chart), stacked_bar_h_label (labeling horizontal bar chart)

    • [ ] https://github.com/vega/vega-lite/issues/7882

  • [ ] https://github.com/vega/vega-lite/issues/7883

    • [x] line_label
    • [x] line_color_label (please rename from line_multi_label)

  • [ ] Examples to consider if we can replace

    • [ ] layer_arc_label
    • [ ] layer_bar_labels_grey
    • [ ] layer_line_lend_label

• [ ] revise padding property (it doesn't feel like what padding means)

• [ ] docs

  • [x] Add a "label" to the "text and tooltip" section in the encoding.md
  • [ ] add these new examples to the example gallery
  • [ ] encoding.label.mark is somehow "Any"

[aantn]

Any updates on this?

[kanitw]

Do we have examples for bar and stacked bar?

[chanwutk]

We don't have it right now, but I can add more.

[sid-kap]

@kanitw I'm really looking forward to this feature, is there anything I can do to help get this feature ready?

[smashmirrorcardboardface]

here also - is there anything we can do to help?

[tmespe]

Is this still being worked on?

[durd07]

Is this still being worked on? It has been opened for so long.