feat: Added support for `weekdayAbbreviations` and `monthAbbreviations` to `MacosDatePicker`

[rklos]

This is another feature from https://github.com/macosui/macos_ui/issues/369. I've added an optional weekdaysAbbreviations and monthsAbbreviations parameters. They allow to change the default English abbreviations in MacosDatePicker.

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]

Done @GroovinChip

[GroovinChip]

@rklos I seem to have mangled the PR when I was doing conflict resolution. I tried to fix that, but apparently I missed something because a date picker test is failing. Do you mind looking over my changes and correcting whatever I did wrong? Thanks.

[rklos]

@GroovinChip you've forgotten to replace _narrowWeekdays

[GroovinChip]

@rklos thank you! So everything is present and working?