[tool] Use swift-format from Xcode (#9460)
As of Xcode 16, swift-format is part of the Xcode distribution. Since CI now uses Xcode 16, we can just always use that version.
This:
- Removes the swift-format-path logic.
- Removes the check for swift-format being available
- Defaults Swift formatting to true only on macOS
- Removes the swift-format CIPD package from .ci.yaml
- Updates Pigeon in packages using Swift Pigeon generation to pick up a fix for a lint issue picked up by the latest version of swift-format (which was already fixed in Pigeon).
Fixes https://github.com/flutter/flutter/issues/153803
## Pre-Review Checklist
[^1]: Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling.
[tool] Use swift-format from Xcode (#9460)
As of Xcode 16, swift-format is part of the Xcode distribution. Since CI now uses Xcode 16, we can just always use that version.
This:
- Removes the swift-format-path logic.
- Removes the check for swift-format being available
- Defaults Swift formatting to true only on macOS
- Removes the swift-format CIPD package from .ci.yaml
- Updates Pigeon in packages using Swift Pigeon generation to pick up a fix for a lint issue picked up by the latest version of swift-format (which was already fixed in Pigeon).
Fixes https://github.com/flutter/flutter/issues/153803
## Pre-Review Checklist
[^1]: Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling.