Unify Android minimum API level to 24 for all runtimes

[sbomer]

Summary

Unify the Android minimum NDK API level to 24 for all runtimes (MonoVM, CoreCLR, NativeAOT), matching what dotnet/runtime already uses.

Motivation

dotnet/runtime builds all runtimes — including MonoVM — against API level 24 (AndroidApiLevelMin=24 in Directory.Build.props). The separate AndroidMinimumNonMonoApiLevel property in dotnet/android was unnecessary since the Mono .so files from runtime were already compiled at API 24 regardless. The only effect of the API 21 setting was selecting older CRT/DSO linker stubs from the NDK sysroot.

Related: dotnet/runtime#126838

Changes

• Bump AndroidMinimumDotNetApiLevel from 21 to 24
• Remove AndroidMinimumNonMonoApiLevel and all related properties, constants, template placeholders, and conditional logic
• Remove nonmono-common-* CMake presets; NativeAOT/CoreCLR presets now inherit from regular common-* presets directly
• Remove ArchToApiLevelNonMono dictionary from XABuildConfig
• Simplify MonoAndroidHelper.GetMinimumApiLevel (no runtime branching)
• Remove MinimumNonMonoApiLevel from GenerateSupportedPlatforms task
• Remove runtime-conditional AndroidMinimumSupportedApiLevel items

[Copilot]

Pull request overview

This PR unifies the Android minimum NDK/API level to 24 across all runtimes (MonoVM, CoreCLR, NativeAOT) and removes the now-redundant “non-mono” minimum API level plumbing throughout build tasks, templates, and native CMake presets.

Changes:

• Bump AndroidMinimumDotNetApiLevel default from 21 → 24 and remove AndroidMinimumNonMonoApiLevel.
• Remove runtime-conditional min-API selection (MSBuild item conditions, GenerateSupportedPlatforms conditional output, XABuildConfig non-mono maps, helper branching).
• Simplify native preset inheritance by dropping nonmono-common-* CMake presets and inheriting from standard common-* presets.

Show a summary per file

File	Description
src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.props.in	Removes runtime-conditional min API items and uses unified NDK API placeholders.
src/Xamarin.Android.Build.Tasks/Xamarin.Android.Build.Tasks.targets	Removes placeholder replacements and task inputs tied to non-mono min API.
src/Xamarin.Android.Build.Tasks/Utilities/MonoAndroidHelper.cs	Simplifies minimum API lookup to a single architecture→API mapping.
src/native/CMakePresets.json.in	Drops nonmono-common-* presets; CoreCLR/NativeAOT inherit from common-* directly.
Configuration.props	Sets unified default AndroidMinimumDotNetApiLevel to 24 and removes non-mono property.
build-tools/xaprepare/xaprepare/xaprepare.targets	Removes generation-time placeholder replacement for the non-mono min API property.
build-tools/xaprepare/xaprepare/Steps/Step_GenerateFiles.cs	Removes non-mono placeholder generation for presets/build config/projitems.
build-tools/xaprepare/xaprepare/ConfigAndData/BuildAndroidPlatforms.cs	Removes non-mono min API accessor; uses unified min API.
build-tools/xaprepare/xaprepare/Application/Properties.Defaults.cs.in	Removes default property wiring for AndroidMinimumNonMonoApiLevel.
build-tools/xaprepare/xaprepare/Application/KnownProperties.cs	Removes AndroidMinimumNonMonoApiLevel constant.
build-tools/Xamarin.Android.Tools.BootstrapTasks/Xamarin.Android.Tools.BootstrapTasks/GenerateSupportedPlatforms.cs	Removes non-mono conditional output generation for supported platforms.
build-tools/scripts/XABuildConfig.cs.in	Removes non-mono minimum API version and non-mono arch→API dictionary.
build-tools/scripts/Ndk.projitems.in	Removes non-mono API-level properties/metadata from NDK projitems.

Copilot's findings

• Files reviewed: 13/13 changed files
• Comments generated: 1

[simonrozsival]

@copilot CI is failing with this root cause analysis, fix it:

Root Cause: Minimum API Level Raised to 24
The branch dev/sbomer/apilevel appears to raise the minimum supported Android API level from 23 to 24. This causes widespread failures:

MAUI Integration build fails with XA4216 because MAUI projects still set SupportedOSPlatformVersion to 23.
Hundreds of MSBuild unit tests fail because test projects build with the default (old) minimum API level and hit FailedBuildException.
Windows Build & Smoke Test has untracked .sarif files from Guardian analysis.

[Copilot]

@copilot CI is failing with this root cause analysis, fix it:

Root Cause: Minimum API Level Raised to 24

...

Fixed in cd8f3e8. The changes address all three CI failure categories:

1. MSBuild unit tests — Updated default SupportedOSPlatformVersion from "21.0" to "24.0" in XamarinAndroidApplicationProject (fixes hundreds of tests that use this default), plus updated all other test files that explicitly set API levels 21/22/23: WearApplicationProject, ManifestTest.cs, PackagingTest.cs, WearTests.cs, GenerateTrimmableTypeMapTests.cs, BuildTest.cs, AndroidGradleProjectTests.cs, and TrimmableTypeMapGeneratorTests.cs. Also updated expected version codes in ManifestTest.cs for version code patterns that include {minSDK}.

2. MAUI Integration XA4216 — Added -p:SupportedOSPlatformVersion=24 to both Debug and Release MAUI template builds in azure-pipelines.yaml to override MAUI's template default (which still sets API 23) while MAUI hasn't yet updated their minimum.

3. NativeAOT sample and DefaultProperties.targets comment updated for consistency.