Queue tab selections during active transitions

[johnsmith507]

Summary

• Queue tab index changes requested while UIKit is still completing a tab transition
• Apply only the latest queued selection after the active transition coordinator finishes
• Preserve rapid tap and swipe requests that currently arrive during a transition and get dropped
• Add an example-app stress launch argument and UI regression for the timer-driven selectedIndex race from Very quick swipes cause app to freeze #52

Fixes #52.

Validation

• git diff --check
• swiftc -typecheck -sdk "$(xcrun --sdk iphonesimulator --show-sdk-path)" -target arm64-apple-ios12.0-simulator -module-name SwipeableTabBarController SwipeableTabBarController/*.swift
• swiftlint lint --config .swiftlint.yml SwipeableTabBarController/SwipeableTabBarController.swift
• xcodebuild test -project Example.xcodeproj -scheme Example -destination 'id=6BC14400-3B60-4343-9DA9-4AF5A72350AC' -derivedDataPath /tmp/swipeable-dd -resultBundlePath /tmp/swipeable-ui.xcresult -only-testing:ExampleUITests/SwipeableTabBarControllerUITests/testRapidProgrammaticTransitionsRemainInteractive

IssueHunt: https://oss.issuehunt.io/r/marcosgriselli/SwipeableTabBarController/issues/52

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IssueHunt Summary

Referenced issues

This pull request has been submitted to:

• #52: Very quick swipes cause app to freeze

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