fix(img): correctly determine when to load image when scrolling quickly on slower devices

[Jacob-McKay]

Fix for this issue: #23703

There is a rare race condition you may experience on devices with slower CPU where the Intersection Observer API supplies multiple items to the callback, instead of only a single element which the previous code assumed it would get. This changes takes the last item (which will be the most current information).

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?

Issue Number: 23703

What is the new behavior?

• Instead of keying off of the first item in the callback to the ion-img Intersection Observer API callback, take the last, most recent one to determine whether the img is on screen and should load

Does this introduce a breaking change?

• Yes
• No

Other information

[liamdebeasi]

Thank you! This is good to merge when the tests pass.

[Jacob-McKay]

Ope, thought I that was a 'complete' button

[liamdebeasi]

Merged. Thank you!