feat: Added support for `startWeekOnMonday` to `MacosDatePicker`

[rklos]

This is the first step in fulfilling all requests from https://github.com/macosui/macos_ui/issues/369. I've added an optional parameter startWeekOnMonday which allows to render a calendar with Monday as a first day of the week.

This is a temporary solution, because the need of this feature is caused by invalid implementation of firstDayOfWeekIndex in flutter_localizations package: https://github.com/flutter/flutter/issues/122274

Pre-launch Checklist

• [X] I have incremented the package version as appropriate and updated CHANGELOG.md with my changes
• [X] I have added/updated relevant documentation
• [X] I have run "optimize/organize imports" on all changed files
• [X] I have addressed all analyzer warnings as best I could

[rklos]

I've added an additional test that checks if startWeekOnMonday is still necessary. This test will fail on customer_testing branch when Flutter has fixed firstDayOfWeekIndex.

[rklos]

Done @GroovinChip

[GroovinChip]

LGTM. Waiting on checks.