permission_handler_windows: lazily create Geolocator

[skylartaylor]

permission_handler_windows currently creates a Windows Geolocator and subscribes to PositionChanged while the plugin is registering. That can make apps appear to access location even when they only depend on permission_handler and never request location.

This PR removes the eager Geolocator member and PositionChanged subscription. Geolocator is now created only inside IsLocationServiceEnabled(), so location service-status checks still work without touching the Windows location API during plugin registration.

Fixes #983.
Fixes #1394.
Related to #1470 and #1389.

Verification performed:

• flutter pub get in permission_handler_windows
• dart format --set-exit-if-changed . in permission_handler_windows
• flutter analyze in permission_handler_windows
• flutter analyze in permission_handler_windows/example
• flutter test in permission_handler_windows reports no test/ directory, so there is no package test suite for this change
• Fork-only Windows smoke: https://github.com/prismplural/flutter-permission-handler/actions/runs/28682163749, example app location registry entries stayed unchanged (0 before launch, 0 after launch)
• Downstream Prism Windows smoke: https://github.com/prismplural/prism-app/actions/runs/28686868188, Prism resolved this fork, built and launched prism_plurality.exe, and location registry entries stayed unchanged (1 before launch, 1 after launch)

Pre-launch Checklist

• I made sure the project builds.
• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or this PR does not need version changes.
• I updated CHANGELOG.md to add a description of the change.
• I updated/added relevant documentation (doc comments with ///), or this PR does not need documentation changes.
• I rebased onto main.
• I added new tests to check the change I am making, or this PR does not need tests.
• I made sure all existing and new tests are passing.
• I ran dart format . and committed any changes.
• I ran flutter analyze and fixed any errors.