[Xamarin.Android.Build.Tasks] Rethink default property values (#9155)

[jonpryor]

Context: 5d1ac0a
Context: dotnet/android-tools@a6a23bb
Context: https://learn.microsoft.com/en-us/visualstudio/mac/what-happened-to-vs-for-mac?view=vsmac-2022

Commit 5d1ac0a had a brilliant idea:

Of particular note is dotnet/android-tools@a6a23bb:
[ed note: now dotnet/android-tools@a6a23bb]

In order to ensure that both Xamarin.Android and the macOS installer
use the same default version numbers for Android SDK components, we are
now using Xamarin.Android.Tools.Versions.props to contain default
version number information. This file is maintained in the
xamarin/xamarin-android-tools repo and will be imported via
external/xamarin-android-tools:

In the intervening four years (!), we've learned something, and the environment has changed.

What we've learned is that this approach is "bump-heavy": in order to update the default value of e.g. $(AndroidSdkPlatformVersion), we'd need to update:

1. dotnet/android-tools
2. xamarin/androidtools
3. Plus other repos that depend on (1) or (2) that are used by (4)
4. xamarin/monodroid
5. dotnet/android

This is, to put it mildly, cumbersome.

Additionally, it's no longer necessary: Visual Studio for Mac will be retired on 2024-Aug-31, so there is no longer a need to have a common file shared between the .NET for Android SDK and Visual Studio for Mac.

Instead of considering Xamarin.Android.Tools.Versions.props as the canonical source of truth:

1. Update Xamarin.Android.Common.targets to now optionally include a new Xamarin.Installer.Common.props file, if present. This will allow e.g. xamarin/android-sdk-installer to eventually provide default property values which are tied to the in-use "Xamarin Manifest" for package installation, e.g. $(AndroidCommandLineToolsVersion), $(JavaSdkVersion).

2. Update Xamarin.Android.Common.props.in so that the following properties are set before importing Xamarin.Android.Tools.Versions.props:

   • $(AndroidCommandLineToolsVersion)
   • $(AndroidNdkVersion)
   • $(AndroidSdkBuildToolsVersion)
   • $(AndroidSdkEmulatorVersion)
   • $(AndroidSdkPlatformVersion)
   • $(AndroidSdkPlatformToolsVersion)
   • $(JavaSdkVersion)

   This will allow us to update these values when this repo ads support for these versions.

Finally, the "Xamarin" manifest is used by the InstallAndroidDependencies target from xamarin/android-sdk-installer, and contains only a select number of Android SDK and JDK versions.

Until android-sdk-installer provides Xamarin.Installer.Common.props, the versions we use need to be in harmony with the Xamarin manifest, so that the InstallAndroidDependencies tests can pass.

Explicitly set $(AndroidNdkVersion)=26.3.11579264, as that's the latest version in the manifest.

[dellis1972]

Looks like the GetDependencyWhenBuildToolsAreMissingTest test needs updating to take this new stuff into account.

build-tools/@SDK_BUILD_TOOLS_VERSION@ should be a dependency.