Migrate from Select.options to Select.selectedOptions (#6678)

* Add selectedOptions as a performance improvement

Move from `options` to `selectedOptions` to reduce code and safe one array traversal.

See https://developer.mozilla.org/en-US/docs/Web/API/HTMLSelectElement/selectedOptions for more information.

Will not work in IE11!

* Remove unnecessary .filter for selected options

Since we moved from `Select.options` to `Select.selectedOptions` we don't need to filter for selected options by ourselfs anymore.

Co-authored-by: Bill <bluebill1049@hotmail.com>

src/logic/getFieldValue.ts

@@ -26,7 +26,7 @@ export default function getFieldValue(_f: Field['_f']) {
   }
 
   if (isMultipleSelect(ref)) {
-    return getMultipleSelectValue(ref.options);
+    return getMultipleSelectValue(ref.selectedOptions);
   }
 
   if (isCheckBox(ref)) {

src/logic/getMultipleSelectValue.ts

@@ -2,5 +2,4 @@ export default (
   options: HTMLOptionElement[] | HTMLOptionsCollection,
 ): string[] =>
   [...options]
-    .filter(({ selected }): boolean => selected)
     .map(({ value }): string => value);