Dispose value notifier in WoltModalSheet

[ulusoyca]

Description

The pageListBuilderNotifier listener should have been disposed properly when the widget is demounted. This causes issues when you launch the modal sheet in the second time. This error is easily reproducible thanks to the well documented issue #226

Before	After
before_dispose_Well.mov	after_dispose_Well.mov

Related Issues

#226

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• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes tests for all changed/updated/fixed behaviors.
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• I updated/added relevant documentation (doc comments with ///).
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Breaking Change

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• Yes, this is a breaking change.
• No, this is not a breaking change.

[github-actions]

Visit the preview URL for this PR (updated for commit 13afb0e):

• https://coffeemakerexample--pr227-dispose-value-notifi-qocqz2jj.web.app
• https://playgroundwoltexample--pr227-dispose-value-notifi-zdd8d3tl.web.app
• https://playgroundnavigator2woltexample--pr227-dispose-value-n-0wbxrnwy.web.app
• https://coffeemakernavigator2--pr227-dispose-value-notifi-1zj7liz4.web.app

_{(expires Wed, 12 Jun 2024 18:37:17 GMT)}

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[TahaTesser]

LGTM!