fix(datetime): update active day styling when day is selected

[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?

Selecting a new day value in the calendar will update the local value, but will not update the visual "active day" of the calendar.

Issue Number: Resolves #24414, #24451

What is the new behavior?

When a new day value is selected, the active day will render correctly.

• The activePartsClone which is used for the isActive calculation, is now updated with the value of the activeParts new value.

Does this introduce a breaking change?

• Yes
• No

Other information

Introduced in #24414

• https://github.com/sean-perkins/gh-24414-datetime-active-day/tree/main (issue is present)
• https://github.com/sean-perkins/gh-24414-datetime-active-day/tree/fix (issue is resolved)

Before	After
Kapture.2021-12-22.at.11.56.52.mp4	Kapture.2021-12-22.at.11.55.15.mp4

[averyjohnston]

Would it make sense to use a @Watch (https://stenciljs.com/docs/reactive-data#watch-decorator) on activeParts to make sure activePartsClone stays updated? That way you wouldn't have to worry about it in so many places.

[sean-perkins]

Would it make sense to use a @Watch (https://stenciljs.com/docs/reactive-data#watch-decorator) on activeParts to make sure activePartsClone stays updated? That way you wouldn't have to worry about it in so many places.

The @Watch approach was much more streamlined, thanks for the suggestion! 👍

Test has been added to validate that setting the active day updates the active day (in the same month).

[averyjohnston]

LGTM!