feat: Make Datetime emit the working parts of the date

### Prerequisites

- [x] I have read the [Contributing Guidelines](https://github.com/ionic-team/ionic-framework/blob/main/docs/CONTRIBUTING.md#creating-an-issue).
- [x] I agree to follow the [Code of Conduct](https://ionicframework.com/code-of-conduct).
- [x] I have searched for [existing issues](https://github.com/ionic-team/ionic-framework/issues) that already include this feature request, without success.

### Describe the Feature Request

There should be an ion-datetime event that gets fired whenever someone commits changes to the month, year, et cetera.

### Describe the Use Case

Some people may want to highlight days per-month in the month view. Currently, one has to submit an entire list of dots for every entry they want to highlight, which is resource intensive with large data sets.

Narrowing the view to the month the person is currently viewing would make this process faster.

### Describe Preferred Solution

an `ionPeek` event with `event.detail.parts` that would include the object that is in `this.workingParts`.

### Describe Alternatives

_No response_

### Related Code

_No response_

### Additional Information

_No response_

Start by locating the ion-datetime implementation and the workingParts state referenced in the request. Trace how month and year changes are committed, then define the event behavior around those changes and verify that its detail exposes the working date parts without requiring a full list of highlighted days.

Written by the indexing model from the issue text.