add more customizable select support

[Calvin-LL]

updated mapping.js according to the description in HTML specs for these elements

• <select>
  • HTML specs: https://html.spec.whatwg.org/multipage/form-elements.html#the-select-element
  • MDN: https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/select
• <optgroup>
  • HTML specs: https://html.spec.whatwg.org/multipage/form-elements.html#the-optgroup-element
  • MDN: https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/optgroup
• <option>
  • HTML specs: https://html.spec.whatwg.org/multipage/form-elements.html#the-option-element
  • MDN: https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/option
• <selectedcontent>
  • HTML specs: https://html.spec.whatwg.org/multipage/form-elements.html#the-selectedcontent-element
  • MDN: https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/selectedcontent

[johnnybenson]

Anything preventing us from merging this?

[MananTank]

Looks good to me - Thanks @Calvin-LL!

[MananTank]

Sorry for the delay here, I was super busy.
This change is out in v1.2.4

[johnnybenson]

Thanks so much!