feat(switch): add slot icons

[mavyfaby]

Fixes #4549

As per issue #4549, I added icon slots in switch component:

Example (icons using slots)

<md-switch icons>
  <md-icon slot="off-icon">
    <svg xmlns="http://www.w3.org/2000/svg" height="24" viewBox="0 -960 960 960" width="24"><path d="M480.028-371q45.428 0 77.2-31.8Q589-434.6 589-480.028t-31.8-77.2Q525.4-589 479.972-589t-77.2 31.8Q371-525.4 371-479.972t31.8 77.2Q434.6-371 480.028-371ZM480-280q-83 0-141.5-58.5T280-480q0-83 58.5-141.5T480-680q83 0 141.5 58.5T680-480q0 83-58.5 141.5T480-280ZM205.5-434.5h-171v-91h171v91Zm720 0h-171v-91h171v91Zm-491-320v-171h91v171h-91Zm0 720v-171h91v171h-91ZM255.761-641.869 147.348-746.522l64.413-67.13 104.13 107.174-60.13 64.609Zm492.478 495.521-105.13-108.174L704-317.652l108.652 104.174-64.413 67.13ZM642.348-704l104.174-108.652 67.13 64.413-107.174 104.13L642.348-704Zm-496 492.239 108.174-105.13L317.652-256 213.478-147.348l-67.13-64.413ZM480-480Z"/></svg>
  </md-icon>
  <md-icon slot="on-icon">
    <svg xmlns="http://www.w3.org/2000/svg" height="24" viewBox="0 -960 960 960" width="24"><path d="M479.958-116.413q-151.477 0-257.511-106.034-106.034-106.034-106.034-257.511 0-151.477 106.046-257.672Q328.505-843.826 480-843.826q13.283 0 26.304.88 13.022.881 25.544 2.881-38.131 29.956-61.076 75.141-22.946 45.185-22.946 97.272 0 91.694 64.325 155.879 64.326 64.186 156.219 64.186 52.608 0 97.413-22.826 44.804-22.826 74.521-60.957 1.761 12.522 2.642 25.235.88 12.712.88 25.896 0 151.435-106.196 257.63-106.195 106.196-257.672 106.196Zm.042-91q81.782 0 147.956-43.717 66.174-43.718 98.413-114.783-17.608 4.044-35.217 6.326-17.609 2.283-34.978 1.805-122.044-4.066-207.946-89.37t-90.446-209.261q-.239-17.369 1.924-34.978t6.446-34.978q-70.826 32.478-114.782 98.652Q207.413-561.543 207.413-480q0 112.929 79.829 192.758Q367.071-207.413 480-207.413Zm-13.109-259.478Z"/></svg>
  </md-icon>
</md-switch>

Off Icon

Dark Mode	Light Mode

On Icon

Dark Mode	Light Mode

Example (default icons fallback)

<md-switch icons></md-switch>

Off Icon

Dark Mode	Light Mode

On Icon

Dark Mode	Light Mode

Example (no icons)

<md-switch></md-switch>

Off Icon

Dark Mode	Light Mode

On Icon

Dark Mode	Light Mode

[asyncLiz]

Thanks for this! Left a bit of feedback :)

[asyncLiz]

Looks great! Thanks a bunch for the contribution