fix(toast, action-sheet): button handler can return Promise<void>

[simonhaenisch]

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Build (npm run build) was run locally and any changes were pushed
• Lint (npm run lint) has passed locally and any fixes were made for failures

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

A toast button can't take an async function that returns Promise<void> as its handler.

Type '() => Promise<void>' is not assignable to type '() => boolean | void | Promise<boolean>'.
  Type 'Promise<void>' is not assignable to type 'boolean | void | Promise<boolean>'.
    Type 'Promise<void>' is not assignable to type 'Promise<boolean>'.
      Type 'void' is not assignable to type 'boolean'. ts(2322)

Issue Number: N/A

What is the new behavior?

• A toast button can take an async function that returns Promise<void> as its handler.

Does this introduce a breaking change?

• Yes
• No

Other information

There might be other button interfaces with this issue...

Update: fixed the same thing for the action sheet (after checking all similar interfaces).

[simonhaenisch]

@liamdebeasi would you mind having a look at this, please?

[brandyscarney]

Thanks! 🙂