Select: Unable to leave loading state without re-render?

[GCHQ-Developer-299]

Summary of the bug

Discovered whileintroducing Playground to ic-select

It seems that the loadingHandler function doesn't consider the loading prop changing to false

  @Watch("loading")
  loadingHandler(newValue: boolean): void {
    newValue && this.triggerLoading();
  }

Additionally, updating the loadingLabel prop doesn't change the loading text until loading is toggled off and back on.

🪜 How to reproduce

Tell us the steps to reproduce the problem:

1. Go to the React Playground storybook in Select (single)
2. click to expand the Select
3. in the controls, toggle 'loading' to true
4. you'll see the select switch to a loading state
5. Toggle 'loading' to false
6. The select won't show results, it remains loading. You'll find that expanding and collapsing the select doesn't fix it

📸 Screenshots or code

🧐 Expected behaviour

Switching loading to false should show results / no results. Also, in the Playgrounds (single/searchable select in React, multi-select in Canary) the loadingLabel should update loading text whenever the prop is changed