[charts][docs] Charts legend rounded symbols

[camerondunford]

The problem in depth

We would like to have rounded legend items as a request from our design team.

There are slots for slotProps.legend.itemMarkWidth & slotProps.legent.itemMarkHeight. Would it be possible to have additional configuration attributes such as slotProps.legend.itemMarkRadius?

e.g.

Setup basic chart with legend. Unable to style the legend symbols beyond height & width.

https://react-wugx2n.stackblitz.io

Your environment

`npx @mui/envinfo`

  System:
    OS: macOS 14.3.1
  Binaries:
    Node: 18.16.0 - ~/.asdf/installs/nodejs/18.16.0/bin/node
    Yarn: 4.1.1 - ~/.asdf/shims/yarn
    npm: 9.5.1 - ~/.asdf/plugins/nodejs/shims/npm
  Browsers:
    Chrome: 123.0.6312.59
    Edge: Not Found
    Safari: 17.3.1
  npmPackages:
    @emotion/react: ^11.11.4 => 11.11.4 
    @emotion/styled: ^11.11.0 => 11.11.0 
    @mui/base:  5.0.0-beta.39 
    @mui/core-downloads-tracker:  5.15.13 
    @mui/icons-material: ^5.15.13 => 5.15.13 
    @mui/lab: ^5.0.0-alpha.168 => 5.0.0-alpha.168 
    @mui/material: ^5.15.13 => 5.15.13 
    @mui/private-theming:  5.15.13 
    @mui/styled-engine:  5.15.11 
    @mui/system:  5.15.13 
    @mui/types:  7.2.13 
    @mui/utils:  5.14.16 
    @mui/x-charts: ^7.0.0-beta.7 => 7.0.0-beta.7 
    @mui/x-data-grid:  6.19.6 
    @mui/x-data-grid-premium: ^6.19.6 => 6.19.6 
    @mui/x-data-grid-pro:  6.19.6 
    @mui/x-date-pickers:  6.19.7 
    @mui/x-date-pickers-pro: ^6.19.7 => 6.19.7 
    @mui/x-license-pro: ^6.10.2 => 6.10.2 
    @types/react: ^18.2.67 => 18.2.67 
    react: ^18.2.0 => 18.2.0 
    react-dom: ^18.2.0 => 18.2.0 
    typescript: ^5.4.2 => 5.4.2 

Search keywords: charts, legend, round Order ID: Secure Code Warrior Premium plan

[trungutt]

We have a little workaround for this issue

<PieChart
  sx={{
    [`& .${legendClasses.mark}`]: {
      ry: 10,
    },
  }}

Credit to @nico1510, but an attribute would be much better

[flaviendelangle]

Whatevers DX we end up having, I think that one is common enough to justify a doc example :+1: cc @alexfauquette

[camerondunford]

Nice. Thank you for the workaround!