Support option clear in select

[Binh-NA]

• only show clear (X) when have value
  

[thien-do]

This is a little bit complicated actually... the type of a Select's value is strictly defined by the consumer, so as library's author we wouldn't know if clicking on "X" should reset the value to "null", "undefined" or something else.

To support this, we should have an explicit prop:

interface SelectProps<T> {
  value?: T;
  reset?: T; // same type of option values
}

but it would be a little bit confusing, as the user may want to reset the value to "undefined" and we can't compare that with when the user doesn't want a reset value.

Need to think about this more