fix(datetime): wheel picker shows consistently in overlays (#29147)

Issue number: resolves #26234

---------

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## What is the current behavior?
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We use an IntersectionObserver to know when each picker column is
visible so we can properly scroll the active option in each column into
view. The IO callback passes an array of entries. Up until this PR, we
have always grabbed the first entry in the array. The problem is that
browsers will sometimes group multiple events into a single array. This
means it's possible to have an event with `isIntersecting: false` and
then another event with `isIntersecting: true` in the same callback.
Since we always grabbed the first event we did not account for the
instances where events were coalesced.

This resulted in column options sometimes not scrolling into view when
presented via an overlay.

## What is the new behavior?
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this PR. -->

- Picker column now grabs the last event in the entries array. This
represents the most recent threshold change.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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## Other information

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screenshots of how the component looks before and after the change. -->

Dev build: `7.7.5-dev.11710347256.1954cae9`

core/src/components/picker-column-internal/picker-column-internal.tsx

@@ -92,7 +92,11 @@ export class PickerColumnInternal implements ComponentInterface {
    */
   componentWillLoad() {
     const visibleCallback = (entries: IntersectionObserverEntry[]) => {
-      const ev = entries[0];
+      /**
+       * Browsers will sometimes group multiple IO events into a single callback.
+       * As a result, we want to grab the last/most recent event in case there are multiple events.
+       */
+      const ev = entries[entries.length - 1];
 
       if (ev.isIntersecting) {
         const { activeItem, el } = this;