[One .NET] improve Install target performance in IDEs

[jonathanpeppers]

.NET 6 needs an equivalent of: 76fb90e

This checks $(BuildingInsideVisualStudio) and skips several targets during SignAndroidPackage.

In .NET 6, the SignAndroidPackage target isn't used because dotnet build produces .apk files. So this shortcut doesn't work, we need an equivalent for Microsoft.Android.Sdk.BuildOrder.targets.

Currently testing .NET 6 with xamarin-android/master, I saw these times for an incremental build of "Hello World" inside VS Windows:

Build 0.890s
Install 0.683s

For comparison, I have seen a command-line build that runs both targets at once get the time:

> dotnet build -t:Run --no-restore
Time Elapsed 00:00:01.07

This was using %MSBUILDNOINPROCNODE%=1, as to replicate the in-memory MSBuild node in Visual Studio.

[jonathanpeppers]

I reviewed a .binlog inside the IDE, and this is actually not an issue.

The correct subset of targets are working in .NET 6:

SignAndroidPackageDependsOn = 
    BuildOnlySettings;
    _CreatePropertiesCache;
    ResolveReferences;
    PrepareResources;
    CreateSatelliteAssemblies;
    _CopyPackage;
    _Sign;