Fill remaining MAUI property-mapper keys

[jonathanpeppers]

Wires up two of the five short-list missing property-mapper keys on the .NET MAUI ⇄ Compose backend and sharpens the inline TODOs for the three remaining keys that genuinely can't be wired without major new work or a new dependency.

Per-handler changes

✅ RefreshViewHandler — now 35 / 35 (100%)

Wires IRefreshView.RefreshColor to the Material 3 PullToRefreshDefaults.Indicator spinner colour:

• Null (or non-SolidPaint) keeps the existing ComposePullToRefreshBox facade path.
• A non-null solid colour switches to a hand-written ColoredIndicatorBox ComposableNode that calls PullToRefreshKt.PullToRefreshBox directly with a custom indicator IFunction3 invoking PullToRefreshDefaults.Instance.Indicator(...) with the packed colour.
• Adds [InternalsVisibleTo("Microsoft.AndroidX.Compose.Maui")] to the Compose facade assembly so the Maui project can reach ComposableLambdas, ComposableLambda0, and BuildModifier.

Sample: RefreshPage.xaml now ships RefreshColor="#FF6B35".

✅ SliderHandler — now 38 / 38 (100%)

Wires ISlider.ThumbImageSource through the shared ImageSourceLoader:

• Small SliderThumbImageSourcePart adapter wraps ISlider as an IImageSourcePart (the slider itself doesn't implement it — only IImage / IImageButton do).
• When the loader resolves a painter or drawable id, BuildNode swaps to a hand-written ImageThumbSlider ComposableNode calling SliderKt.Slider(value, onValueChange, ..., thumb = { ... }) directly with a ComposeImage of the resolved source in the thumb slot. Material 3's stock Slider draws its thumb as a fixed circle and has no public way to inject a custom drawable, so the lower-level overload is required.

Sample: SlidersPage.xaml now ships a third slider with ThumbImageSource="dotnet_bot.png".

Held back with sharpened TODO reasons

🟡 ScrollViewHandler.{Horizontal,Vertical}ScrollBarVisibility — still 33 / 35 (94%)

Compose Foundation 1.9 / 1.10 / 1.11 (and the Material3 layer on top) don't expose any public Scrollbar / scrollbar API on Android. The androidx.compose.foundation.v2.scrollbar extension exists only on the Multiplatform desktop target; Modifier.verticalScroll / horizontalScroll have no scrollbar-visibility flag at all. Honouring even the Default / Always / Never enum requires a hand-built ScrollState + animated overlay drawn into a sibling Box — meaningful surgery and a non-trivial new public surface. TODO comment refined to spell this out.

🟡 ImageHandler.IsAnimationPlaying / ImageButtonHandler.IsAnimationPlaying — still 33 / 34 (97%) and 37 / 38 (97%)

ImageSourceLoader rasterises the resolved Drawable to a static Bitmap (via DrawableKt.ToBitmap) before wrapping it as a BitmapPainter. The Android-native AnimatedImageDrawable (API 28+) keeps animating, but the snapshot we hand to Compose doesn't — its first frame is what gets sampled. Fixing this needs either:

• a hand-rolled DrawablePainter JCW subclass of androidx.compose.ui.graphics.painter.Painter whose DrawScope.onDraw forwards into Drawable.draw(Canvas) and toggles start() / stop() based on the slot, or
• routing source resolution through coil-compose's AsyncImagePainter.

Both are larger surgery + a real new dependency. TODO comments refined to spell this out.

Headline coverage

Metric	Before	After
Property-mapper keys covered	883 / 1224 (72.1%)	885 / 1224 (72.3%)
Containers category	165 / 174 (95%)	167 / 174 (96%)
Leaves category	683 / 695 (98%)	685 / 695 (99%)
Handlers at ✅ 100%	(before: RefreshView 97%, Slider 97% — both 🟡)	RefreshView and Slider now ✅

Per-handler delta: RefreshViewHandler 34/35 → 35/35, SliderHandler 37/38 → 38/38, both moving from 🟡 to ✅.

Verifying

dotnet build src/Microsoft.AndroidX.Compose.Maui                    # facade only
dotnet build src/Microsoft.AndroidX.Compose.Maui.Sample             # full sample, deploys gallery
dotnet run scripts/maui-coverage.cs                                 # regenerate docs/maui-coverage.md

Each commit is independently revertable: Wire RefreshColor on RefreshViewHandler, Wire ThumbImageSource on SliderHandler, Sharpen TODO reasons for unmapped handler keys.

[Copilot]

Pull request overview

This PR fills two of the five remaining unmapped MAUI property-mapper keys on the Compose backend and refines the inline TODO comments for the three keys that cannot be wired without major new work or dependencies.

Changes:

• Wires IRefreshView.RefreshColor by introducing a hand-written ColoredIndicatorBox ComposableNode that calls the bound PullToRefreshKt.PullToRefreshBox directly with a custom indicator slot piping the packed color through PullToRefreshDefaults.Indicator. Adds [InternalsVisibleTo("Microsoft.AndroidX.Compose.Maui")] to expose internal helpers like ComposableLambdas.Wrap3, ComposableLambda0, and Modifier.Build().
• Wires ISlider.ThumbImageSource through the shared ImageSourceLoader via a SliderThumbImageSourcePart adapter, with an ImageThumbSlider ComposableNode that calls the lower-level SliderKt.Slider(..., thumb = {...}) overload directly to render a custom thumb image.
• Sharpens TODO comments for ScrollViewHandler.{Horizontal,Vertical}ScrollBarVisibility and ImageHandler/ImageButtonHandler.IsAnimationPlaying with concrete technical reasons why they can't be wired yet.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/Microsoft.AndroidX.Compose/AssemblyInfo.cs	New [InternalsVisibleTo("Microsoft.AndroidX.Compose.Maui")] to expose internal helpers to the MAUI handler assembly.
src/Microsoft.AndroidX.Compose.Maui/Handlers/RefreshViewHandler.cs	Adds MapRefreshColor mapper, _refreshColor state, and ColoredIndicatorBox inner class for custom-color spinner rendering.
src/Microsoft.AndroidX.Compose.Maui/Handlers/SliderHandler.cs	Adds MapThumbImageSource mapper, lazy ImageSourceLoader, SliderThumbImageSourcePart adapter, and ImageThumbSlider inner class for custom thumb image rendering.
src/Microsoft.AndroidX.Compose.Maui/Handlers/ScrollViewHandler.cs	Refines TODO comment explaining why scrollbar visibility can't be wired (no public Scrollbar API on Android Compose).
src/Microsoft.AndroidX.Compose.Maui/Handlers/ImageHandler.cs	Refines TODO comment explaining why IsAnimationPlaying can't be wired (static BitmapPainter, needs DrawablePainter or coil-compose).
src/Microsoft.AndroidX.Compose.Maui/Handlers/ImageButtonHandler.cs	Same TODO refinement as ImageHandler for IsAnimationPlaying.
src/Microsoft.AndroidX.Compose.Maui.Sample/Pages/SlidersPage.xaml	Adds a third slider demo with ThumbImageSource="dotnet_bot.png".
src/Microsoft.AndroidX.Compose.Maui.Sample/Pages/SlidersPage.xaml.cs	Adds value-change handler and reset logic for the thumb-image slider.
src/Microsoft.AndroidX.Compose.Maui.Sample/Pages/RefreshPage.xaml	Adds RefreshColor="#FF6B35" and updates labels to describe the new coverage.
docs/maui-coverage.md	Auto-generated coverage report reflecting the two new mappings (883→885 keys, RefreshView and Slider now ✅).