fix(datetime): confirm method now uses selected date

[sean-perkins]

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Build (npm run build) was run locally and any changes were pushed
• Lint (npm run lint) has passed locally and any fixes were made for failures

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

When confirming the date using datetime's confirm() method, it will use the working parts (visible calendar month) instead of the active parts (selected calendar month). This results in incorrect date values when a user selects a date, navigates next/previous to a different calendar month and uses the confirm() API to close/dismiss the datetime overlay.

Issue URL: #24823

What is the new behavior?

• The confirm() API uses the active parts when setting the current value.
• Navigating to next/previous months will not affect the date value when using confirm(), unless the user selects a new date inside that month.

Does this introduce a breaking change?

• Yes
• No

Other information

[averyjohnston]

LGTM once Liam's comment is addressed 👍