Ensure no existing parent is present before adding to container

[kiftio]

What changes are you making?

CLOSES #127

When preloading is enabled and we fetch the checkout web view from the cache, there are some scenarios where we try to add the fetched view to a parent container when it already has a parent (causing an IllegalStateException).

This can be reproduced by enabling preloading, then calling present() twice without dismissing the modal (there also may be other cases).

This PR looks to ensure the webView has no existing parent before we add it to its container.

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Note: When we remove checkout web views from their container, we also look to ensure it's destroyed if we think it will not be used again, to avoid memory leaks. We don't want to do this destroy/cleanup in this case, as the view will be added to the view hierarchy shortly after removing the existing parent and therefore must not be destroyed.

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How to test

Add the following below ShopifyCheckoutSheetKit.present(url, activity, eventProcessor) in the MobileBuyIntegration samples CartViewModel to trigger a delayed second present call.

Handler(Looper.getMainLooper()).postDelayed({
     ShopifyCheckoutSheetKit.present(url, activity, eventProcessor)
}, 500)

Repeat on main and on this branch.

Before you merge

Important

• I've added tests to support my implementation
• I have read and agree with the Contribution Guidelines.
• I have read and agree with the Code of Conduct.
• I've updated the README.

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Checklist for releasing a new version

• I have bumped the version number in the build.gradle file
• I have added a Changelog entry.
• I have updated the versions in the README.md for both Gradle and Maven.

Tip

See the Contributing documentation for instructions on how to publish a new version of the library.

[markmur]

Looks good 👍