Implement VerticalTextAlignment on text-input handlers

[jonathanpeppers]

Summary

Wires VerticalTextAlignment on the five Compose-backed text-input handlers — LabelHandler, EntryHandler, EditorHandler, SearchBarHandler, PickerHandler — so each goes from 98% → 100% in docs/maui-coverage.md.

Coverage delta

Headline	Before	After
Property-mapper keys covered	883 / 1224 (72.1%)	888 / 1224 (72.5%)
Leaves category	684 / 695 (98%)	689 / 695 (99%)
LabelHandler	39 / 40 (98%)	✅ 40 / 40 (100%)
EntryHandler	48 / 49 (98%)	✅ 49 / 49 (100%)
EditorHandler	45 / 46 (98%)	✅ 46 / 46 (100%)
SearchBarHandler	46 / 47 (98%)	✅ 47 / 47 (100%)
PickerHandler	40 / 41 (98%)	✅ 41 / 41 (100%)

Approach

Compose's Modifier.wrapContentHeight(align) measures the child without imposing the parent's min height, then aligns the child within the parent's allocated height. That's exactly the semantic MAUI's VerticalTextAlignment carries — visible only when the control has more height than it naturally needs.

1. New JNI overload — ComposeBridges.ModifierWrapContentHeightAligned(IntPtr, IAlignmentVertical?, bool). Reuses the existing ModifierWrapContentHeightDefault enum (slot 0 = align, slot 1 = unbounded) so the auto-default-mask clears bit 0 only when the C# caller passes a non-null alignment. The pre-existing ModifierWrapContentHeight(IntPtr, bool) overload is untouched (still defaults to Kotlin's CenterVertically).
2. C# entry points — new Modifier.WrapContentHeight(Alignment.Vertical, bool) static factory + extension method. Public-API entries added to PublicAPI.Unshipped.txt.
3. MAUI helper — Microsoft.AndroidX.Compose.Maui.Platform.VerticalAlignmentMapping converts Microsoft.Maui.TextAlignment → Alignment.Vertical (Start→Top, Center→CenterVertically, End→Bottom, Justify→Top — Compose has no vertical-justify analog, matching the stock Android backend).
4. Per-handler wiring — each handler gains a _vTextAlign MutableState<int> slot, a MapVerticalTextAlignment mapper entry, and .ApplyVerticalTextAlignment(vAlign) chained onto its outer modifier (after ApplySemantics). The five // TODO: VerticalTextAlignment … comments are deleted.

Sample

Adds VerticalAlignmentPage to Microsoft.AndroidX.Compose.Maui.Sample — one page exercising VerticalTextAlignment="Start|Center|End" on each of the five controls inside fixed-height frames so the difference is obvious. Wired into HomePage + AppShell under route vertical-align.

Verification

• dotnet build src/Microsoft.AndroidX.Compose — 0 errors, no new warnings.
• dotnet build src/Microsoft.AndroidX.Compose.Maui — 0 errors, 0 warnings.
• dotnet build src/Microsoft.AndroidX.Compose.Maui.Sample — 0 errors, 0 warnings.
• dotnet run scripts/maui-coverage.cs — regenerated docs/maui-coverage.md; all five handlers ✅ 100%.

[Copilot]

Pull request overview

This PR wires VerticalTextAlignment support onto the five Compose-backed MAUI text-input handlers (LabelHandler, EntryHandler, EditorHandler, SearchBarHandler, PickerHandler), moving each from 98% to 100% property-mapper coverage. The approach uses Compose's Modifier.wrapContentHeight(Alignment.Vertical) to position text content within a parent slot, which is the correct semantic match for MAUI's VerticalTextAlignment property.

Changes:

• Adds a new ComposeBridges.ModifierWrapContentHeightAligned JNI bridge and corresponding Modifier.WrapContentHeight(Alignment.Vertical, bool) public API (static factory + extension), reusing the existing ModifierWrapContentHeightDefault enum.
• Introduces VerticalAlignmentMapping (internal helper in the MAUI project) to convert Microsoft.Maui.TextAlignment → Alignment.Vertical and chain the modifier, then wires _vTextAlign MutableState<int> + MapVerticalTextAlignment + ApplyVerticalTextAlignment onto all five handlers with consistent patterns.
• Adds a VerticalAlignmentPage XAML sample exercising all five controls with Start/Center/End inside fixed-height frames, and updates docs/maui-coverage.md to reflect the new 100% coverage.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/Microsoft.AndroidX.Compose/ComposeBridges.cs	New ModifierWrapContentHeightAligned bridge with explicit IAlignmentVertical? param
src/Microsoft.AndroidX.Compose/ModifierExtensions.cs	New WrapContentHeight(Alignment.Vertical, bool) extension method with null check
src/Microsoft.AndroidX.Compose/Modifier.cs	Static factory overload delegating to the extension; fixes inheritdoc cref for disambiguation
src/Microsoft.AndroidX.Compose/PublicAPI.Unshipped.txt	Two new entries for the public overload (static + extension)
src/Microsoft.AndroidX.Compose.Maui/Platform/VerticalAlignmentMapping.cs	New internal mapping helper: TextAlignment → Alignment.Vertical + modifier extension
src/Microsoft.AndroidX.Compose.Maui/Handlers/LabelHandler.cs	Adds _vTextAlign slot, mapper, and modifier chaining; removes TODO comment
src/Microsoft.AndroidX.Compose.Maui/Handlers/EntryHandler.cs	Same wiring pattern as LabelHandler (default Center)
src/Microsoft.AndroidX.Compose.Maui/Handlers/EditorHandler.cs	Same wiring pattern (default Start for multi-line)
src/Microsoft.AndroidX.Compose.Maui/Handlers/SearchBarHandler.cs	Same wiring pattern (default Center)
src/Microsoft.AndroidX.Compose.Maui/Handlers/PickerHandler.cs	Same wiring pattern (default Center)
src/Microsoft.AndroidX.Compose.Maui.Sample/Pages/VerticalAlignmentPage.xaml	XAML demo exercising Start/Center/End on all 5 controls in fixed-height frames
src/Microsoft.AndroidX.Compose.Maui.Sample/Pages/VerticalAlignmentPage.xaml.cs	Code-behind seeding Picker items
src/Microsoft.AndroidX.Compose.Maui.Sample/HomePage.xaml.cs	Demo registry entry
src/Microsoft.AndroidX.Compose.Maui.Sample/AppShell.xaml.cs	Route registration for vertical-align
docs/maui-coverage.md	Coverage numbers updated to reflect 100% on all 5 handlers