[iOS] Fix missing partial columns in horizontal grid layout

[hartez]

Description of Change

These changes work around a UICollectionViewFlowLayout issue where horizontally-scrolling grid layouts do not display the last column if it is only partial.

These changes also fix an issue where the CollectionView does not respect the Page's safe area settings on iOS 11+ (which had a side-effect of incorrectly laying out columns in landscape mode).

Issues Resolved

• fixes [Bug] CollectionView (iOS) using horizontal grid does not display last column of uneven item count #6077

API Changes

None

Platforms Affected

• iOS

Behavioral/Visual Changes

None

Before/After Screenshots

Not applicable

Testing Procedure

Issue 6077 in Control Gallery (automated).

PR Checklist

• Has automated tests
• Rebased on top of the target branch at time of PR
• Changes adhere to coding standard
• Boxes checked

[rmarinho]

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[rmarinho]

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[samhouts]

@hartez Test fails on Android :(

[hartez]

Failing iOS tests are utterly unrelated.