This changes the border into a linear gradient background image which allows us to avoid the height decrease on press and have the same border as the background color when pressed.
- merges all action sheet tests to the basic directory (except standalone, translucent), references #16715
- removes the height shift on press, fixes#16790
- fixes the cancel button on iOS so it is `#ffffff` by default
- gets the look of the action sheet closer to native for iOS
- only applies the translucent and backdrop filter if it is supported by the browser (chrome will not show transparent anymore)
- updates documentation to describe when translucent will show up
- adds documentation on how to use screenshot tests
