Matthew Kosarek fe409cfca4
Implement dialog windows for the win32 platform (#176309)
## What's new?
- Implemented `DialogWindowControllerWin32` for win32 dialogs 🚀
- Refactored and updated the Win32 embedder to support dialogs
- Updated the `multiple_windows` example to demonstrate both modal and
modeless dialogs
- Added integration tests for the dialog windows
- Added tests for dialogs in the embedder

## How to test?
1. Run the `multiple_windows` example application with a local engine
built from this pull request
2. Click the `Modeless Dialog` creation button on the main window
3. Open a regular window and click the `Modal Dialog` creation button
4. Note the behavior of modal and modeless dialogs

## 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.
- [x] 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.
2025-10-16 15:32:29 +00:00
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