[Issue-21] Expose minimumTopOffset

[mpospese]

Introduction

PWC may need fine-tuned control over the maximum size of bottom sheets. We had a private constant that controlled this, but now it's a public variable that's part of the sheet's appearance.

Purpose

Fix #21 Move the private minimumTopOffset constant from BottomSheetController to Appearance and make it a public variable.

Scope

• Move the minimumTopOffset property
• Make BottomSheetController.minimumContentHeight public
• Refactor BottomSheetController to better organize the code

Discussion

The issue says to also move minimumContentHeight to Appearance, but it is already there serving a related but slightly different purpose, so I just switched it from private let to public var in BottomSheetController.

There are also a few cleanup items I did:

1. mark the init(coder:) methods as unavailable and removed their unit tests
2. added a helper file to tests for comparing Typography equality
3. improved the unit tests around the appearance
4. renamed memory leak tracking method for consistency

📱 Screenshots

Sheet appearance is unchanged.

📈 Coverage

Code

100%

Documentation

100%