Revert "Fix SwipeItem IconImageSource color handling and rendering across platforms (#35632)"

[kubaflo]

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Supersedes #36883, which was branched off main while targeting inflight/candidate. That mismatch dragged in 42 unrelated main-only commits and produced four spurious conflicts in files that have nothing to do with SwipeItem. This branch is built directly on inflight/candidate, so it is a clean single-commit diff.

Issue Details

This reverts #35632 ("Fix SwipeItem IconImageSource color handling and rendering across platforms") from the .NET 10 servicing line.

#35632 stopped auto-tinting SwipeItem.IconImageSource for PNG/SVG sources, so those icons now render in their own colors instead of a contrast color derived from the item background. It shipped in 10.0.90 (SR9) and is causing #36766 — an SVG icon whose fill is #212121 now renders black on a black swipe item in dark mode, i.e. effectively invisible.

The change is a reasonable direction, but it is too breaking for a servicing release:

• It removes a legibility guarantee with no replacement. GetTextColor() picks white or black from background luminosity. Fix SwipeItem IconImageSource color handling and rendering across platforms #35632 removed that for PNG/SVG but left it in place for the item's label text, so the text is still contrast-corrected while the icon is not.
• There is no opt-in. [Android] SwipeItem IconImageSource should allow more configuration #23074 was labelled proposal/open and asked for more configuration; what shipped was a behavior change with none. An affected app's only options today are pinning to 10.0.80 or re-authoring every SVG per theme.
• It compounds with Fix SwipeItem background not updating on AppTheme change #36271 (also SR9), which makes BackgroundColor correctly follow AppThemeBinding. Before SR9 the stale light background accidentally preserved contrast; together the two changes produce black-on-black.
• The prior behavior was the Xamarin.Forms behavior, not an inconsistency — Xamarin tinted every icon unconditionally on both Android (SwipeViewRenderer.cs#L858) and iOS (SwipeViewRenderer.cs#L713).

Description of Change

git revert of c78acfe, restoring the previous behavior on all platforms:

• Android — SetColorFilter(GetTextColor(), SrcAtop) applied to every drawable again
• iOS/Mac — AlwaysTemplate rendering mode on every image again, with TintColor = fontImageSource.Color ?? GetTextColor()
• Windows — MapSourceAsync back to ToIconSource() (BitmapIconSource, whose ShowAsMonochrome defaults to true); the LoadFileIconAsync helper is removed

The Issue23074 host-app page, shared test, cancel_red.svg and the SwipeItemFontAndSvgIconsRenderCorrectly snapshots are removed with it, and the SwipeView snapshots are restored to their pre-#35632 baselines.

The revert is scoped strictly to #35632. MapVisibility on the Windows handler — added on inflight/candidate after #35632 — is untouched.

Conflict resolution note: TestCases.iOS.Tests/snapshots/ios/VerifyCollectionViewContentWithIconImageSwipeItem.png conflicted because #36202 re-saved it for iOS 18 after #35632 landed. That test's swipe item has BackgroundColor = #6A5ACD (luminosity ≈ 0.40 → white), so with this revert groceries.png is tinted solid white again and the pre-#35632 baseline is the correct content. If iOS 18 CI shows drift unrelated to the tint, this one snapshot may need a re-save from the CI artifact.

Follow-up

The behavior change itself is good and should ship — just in .NET 11 rather than servicing, paired with an explicit opt-in API so users get a real migration path instead of a silent rendering change in a patch release. That is #36884, which keeps the #35632 behavior and adds SwipeItem.IconColor.

Issues Fixed

Fixes #36766

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