MultiSelect[Field] improvements

[techniq]

• Support overriding Apply/Cancel buttons
  • Useful for i18n support, along with changing button style (variant="fill" vs "variant="fill-light", etc)
  • Maybe add a listActions slot, or have actions override all actions?
  • Should on:click (applying) be moved to a surrounding <form>? Does this impact a high level <form> if so (stopPropagation?)
  • See: Consistent and configurable OK/Cancel buttons #240
• Support applying immediately on check (how does that effect showing the selected items at the top)
• Support applying on Menu blur (MultiSelectField only)
• Improve accessibility
  • Keyboard up/down and enter to select (similar to SelectField)
• Prop to show selections as chips
  • Icon to remove (x)
  • Backspace
  • Examples
    • https://multiselect.janosh.dev/
    • https://flowbite-svelte.com/docs/forms/select#MultiSelect
    • https://carbon-components-svelte.onrender.com/components/MultiSelect
    • https://react-select.com/home
    • https://mui.com/material-ui/react-select/#chip

See discussion for some context

[techniq]

mode="immediate" along with maintainOrder props are now available in 0.71.3