Feat: Allow Normalized Theta Tooltip

[lsh]

Handles #8301, allows for the use of normalized percentage tooltips in theta encodings.

[kanitw]

Add arc_pie_normalize_tooltip.vl.json as an example?

• You can copy arc_pie.vl.json in examples/specs
• Under "Circular Plots" in examples.json, add

{
        "name": "arc_pie_normalize_tooltip",
        "title": "Pie Chart with percentage_tooltip"
      },

• Modify arc.md to include this example

[kanitw]

To make this section read smoothly, I wonder if it's worth adding arc_pie_tooltip to say

{:#tooltip}
### Pie Charts with Tooltips

To add tooltip, you can set `tooltip: true` in `mark`


<span class="vl-example" data-name="arc_pie_tooltip"></span>

By default, the tooltip will show actual value of the theta field. 
Alternatively, ... 

(The tooltip anchor is for the suggested link in the stack doc)

[lsh]

Would this replace the note text on line 68 as well?

[kanitw]

Would this replace the note text on line 68

I don't think so. That's about labeling. (That said, we can add

### Pie Charts with Labels above that part too so the doc looks like having more structure

[kanitw]

Probably worth adding "and pie charts [with percentage tooltip](https://vega.github.io/vega-lite/docs/arc.html#tooltip)" in the parentheses for

• "normalize" - stacking with normalized domain (for creating normalized stacked bar and area charts)

[lsh]

Closed in favor of #8308