Suppress previous route transition if current route is fullscreenDialog

[MitchellGoodwin]

Fixes #159289

Cupertino and Material routes were looking to see if the next route was a full screen dialog route, and not transitioning accordingly. However with the updates to allow mixed transitions in an app, any route will try and transition if a delegatedTransition is available. This PR makes it so that Cupertino and Material routes that are fullscreen dialogs will use canTransitionFrom to tell the previous route not to transition.

Before: 388677067-d301238d-6615-42a7-b60a-611c61136d88.webm

After:

https://github.com/user-attachments/assets/7deb5143-cd67-4696-95ec-9d7df329dfa4

Pre-launch Checklist

• [x] I read the Contributor Guide and followed the process outlined there for submitting PRs.
• [x] I read the Tree Hygiene wiki page, which explains my responsibilities.
• [x] I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• [x] I signed the CLA.
• [x] I listed at least one issue that this PR fixes in the description above.
• [ ] I updated/added relevant documentation (doc comments with ///).
• [x] I added new tests to check the change I am making, or this PR is test-exempt.
• [x] I followed the breaking change policy and added Data Driven Fixes where supported.
• [x] All existing and new tests are passing.

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