fix(datetimepickerv2): make sure locale is 2 letters

[jessieyan]

Closes #3757

Summary

• We need to make sure locale is 2 letters. If use passes in locale like "en-us", we make sure we use en instead of en-us

Change List (commits, features, bugs, etc)

• Add locale checks for DateTimePicker and DateTimePickerv2

Acceptance Test (how to verify the PR)

• go to single select story
• change locale to 'en-us'
• make sure no errors show up in the console

Regression Test (how to make sure this PR doesn't break old functionality)

• tests here

Things to look for during review

• [ ] Make sure all references to iot or bx class prefix is using the prefix variable
• [ ] (React) All major areas have a data-testid attribute. New test ids should have test written to ensure they are not changed or removed.
• [ ] UI should be checked in RTL mode to ensure the proper handling of layout and text.
• [ ] All strings should be translatable.
• [ ] The code should pass a11y scans (The storybook a11y knob should show no violations). New components should have a11y test written.
• [ ] Unit test should be written and should have a coverage of 90% or higher in all areas.
• [ ] All components should be passing visual regression test. For new styles or components either a visual regression test should be written for all permutations or the base image updated.
• [ ] Changes or new components should either write new or update existing documentation.
• [ ] PR should link and close out an existing issue

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