[Android] Fix CollectionView items not resizing after orientation change on Shell pages

[SyedAbdulAzeemSF4852]

Note

Are you waiting for the changes in this PR to be merged?
It would be very helpful if you could test the resulting artifacts from this PR and let us know in a comment if this change resolves your issue. Thank you!

Issue Details

• When a CollectionView page is opened in portrait mode, then the user navigates to another page, rotates to landscape, and navigates back — the CollectionView items display with portrait dimensions. Only after scrolling do they resize correctly.

Root Cause

• When navigating away from a CollectionView page in Shell, the page's handler and RecyclerView are reused. If the device rotates while the page is off-screen, Android skips invalidating hidden views, so the children remain marked as "clean". When navigating back, LinearLayoutManager skips remeasuring these "clean" children, causing items to display with portrait dimensions in landscape. As a result, items render at the wrong size until a scroll forces a re-measure.

Description of Change

• MauiRecyclerView.cs: Added OnSizeChanged() override. Guard: oldw > 0 && oldh > 0 && (Math.Abs(w - oldw) > 1 || Math.Abs(h - oldh) > 1).Calls InvalidateItemMeasures() which: (a) calls adapter.ClearMeasureCache(), (b) iterates visible children calling itemContentView.InvalidateCachedSize() + itemContentView.ForceLayout()
• ItemsViewAdapter.cs: Added internal virtual void ClearMeasureCache()
• StructuredItemsViewAdapter.cs: internal override void ClearMeasureCache() sets _size = null
• ItemContentView.cs: Added internal void InvalidateCachedSize() — resets _pixelSize = null, _previousPixelWidth = -1, _previousPixelHeight = -1
• PublicAPI.Unshipped.txt: Added OnSizeChanged override entry

Issues Fixed

Fixes #19667
Fixes #31892

Validated the behaviour in the following platforms

• Windows
• Android
• iOS
• Mac

Output

Before	After
Before.mov	After.mov