Add tooltip windows to the windowing API alongside the window positioning logic

[mattkae]

What's new?

• Added tooltips to the windowing API, but they have no implementation for the time being
• Added the WindowPostiioner logic to the windowing API
• Wrote a lot of tests 🧪

Pre-launch Checklist

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

[gemini-code-assist]

Code Review

This pull request introduces tooltip windows to the windowing API, along with the logic for positioning them. A significant amount of new code has been added, including the TooltipWindowController, TooltipWindow widget, and the WindowPositioner logic. A comprehensive suite of tests for the new window positioning logic has also been included.

My review focuses on improving code clarity, consistency, and maintainability. I've pointed out a few documentation typos and copy-paste errors, including a misleading error message in the Win32 implementation. I've also suggested a minor refactoring in the WindowPositioner to improve code readability and reduce redundancy. Overall, this is a solid addition with good test coverage.

[justinmc]

Overall looks good. This kind of positioning stuff is fiddly but I think your way of doing things keeps it pretty clean.

My main concern is with the use of GlobalKeys in the example and how that should be done in the ideal situation, because I want to make sure we set users up to be able to get this right on the happy path.

I see that the framework is positioning the tooltip based on constraints from the platform. Just to make sure, do all platforms provide this kind of constraint size information?

[justinmc]

LGTM 👍

I'm on board with the WindowPositionerAnchor enum instead of Alignment, especially given that it more closely maps to Waylands implementation. Thanks for all of the changes.